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*-. Merge branches 'doc.2021.07.20c', 'fixes.2021.08.06a', 'nocb.2021.07.20c', ↵Paul E. McKenney2021-08-101-74/+33
|\ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'nolibc.2021.07.20c', 'tasks.2021.07.20c', 'torture.2021.07.27a' and 'torturescript.2021.07.27a' into HEAD doc.2021.07.20c: Documentation updates. fixes.2021.08.06a: Miscellaneous fixes. nocb.2021.07.20c: Callback-offloading (NOCB CPU) updates. nolibc.2021.07.20c: Tiny userspace library updates. tasks.2021.07.20c: Tasks RCU updates. torture.2021.07.27a: In-kernel torture-test updates. torturescript.2021.07.27a: Torture-test scripting updates.
| | * rcu/nocb: Remove NOCB deferred wakeup from rcutree_dead_cpu()Frederic Weisbecker2021-07-201-3/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | At CPU offline time, we must handle any pending wakeup for the nocb_gp kthread linked to the outgoing CPU. Now we are making sure of that twice: 1) From rcu_report_dead() when the outgoing CPU makes the very last local cleanups by itself before switching offline. 2) From rcutree_dead_cpu(). Here the offlining CPU has gone and is truly now offline. Another CPU takes care of post-portem cleaning up and check if the offline CPU had pending wakeup. Both ways are fine but we have to choose one or the other because we don't need to repeat that action. Simply benefit from cache locality and keep only the first solution. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu/nocb: Start moving nocb code to its own plugin fileFrederic Weisbecker2021-07-201-0/+1
| |/ |/| | | | | | | | | | | | | | | | | | | | | | | | | The kernel/rcu/tree_plugin.h file contains not only the plugins for preemptible RCU, but also many other features including rcu_nocbs callback offloading. This offloading has become large and complex, so it is time to put it in its own file. This commit starts that process. Suggested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> [ paulmck: Rename to tree_nocb.h, add Frederic as author. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Replace deprecated CPU-hotplug functionsSebastian Andrzej Siewior2021-08-101-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The functions get_online_cpus() and put_online_cpus() have been deprecated during the CPU hotplug rework. They map directly to cpus_read_lock() and cpus_read_unlock(). Replace deprecated CPU-hotplug functions with the official version. The behavior remains unchanged. Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: rcu@vger.kernel.org Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Use per_cpu_ptr to get the pointer of per_cpu variableLiu Song2021-08-061-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | There are a few remaining locations in kernel/rcu that still use "&per_cpu()". This commit replaces them with "per_cpu_ptr(&)", and does not introduce any functional change. Reviewed-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Reviewed-by: Neeraj Upadhyay <neeraju@codeaurora.org> Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org> Signed-off-by: Liu Song <liu.song11@zte.com.cn> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Remove useless "ret" update in rcu_gp_fqs_loop()Liu Song2021-08-061-2/+2
| | | | | | | | | | | | | | | | | | | | Within rcu_gp_fqs_loop(), the "ret" local variable is set to the return value from swait_event_idle_timeout_exclusive(), but "ret" is unconditionally overwritten later in the code. This commit therefore removes this useless assignment. Signed-off-by: Liu Song <liu.song11@zte.com.cn> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Make rcu_gp_init() and rcu_gp_fqs_loop noinline to conserve stackPaul E. McKenney2021-08-061-2/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | The kbuild test project found an oversized stack frame in rcu_gp_kthread() for some kernel configurations. This oversizing was due to a very large amount of inlining, which is unnecessary due to the fact that this code executes infrequently. This commit therefore marks rcu_gp_init() and rcu_gp_fqs_loop noinline_for_stack to conserve stack space. Reported-by: kernel test robot <lkp@intel.com> Tested-by: Rong Chen <rong.a.chen@intel.com> [ paulmck: noinline_for_stack per Nathan Chancellor. ] Reviewed-by: Nathan Chancellor <nathan@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Weaken ->dynticks accesses and updatesPaul E. McKenney2021-08-061-8/+18
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Accesses to the rcu_data structure's ->dynticks field have always been fully ordered because it was not possible to prove that weaker ordering was safe. However, with the removal of the rcu_eqs_special_set() function and the advent of the Linux-kernel memory model, it is now easy to show that two of the four original full memory barriers can be weakened to acquire and release operations. The remaining pair must remain full memory barriers. This change makes the memory ordering requirements more evident, and it might well also speed up the to-idle and from-idle fastpaths on some architectures. The following litmus test, adapted from one supplied off-list by Frederic Weisbecker, models the RCU grace-period kthread detecting an idle CPU that is concurrently transitioning to non-idle: C dynticks-from-idle { DYNTICKS=0; (* Initially idle. *) } P0(int *X, int *DYNTICKS) { int dynticks; int x; // Idle. dynticks = READ_ONCE(*DYNTICKS); smp_store_release(DYNTICKS, dynticks + 1); smp_mb(); // Now non-idle x = READ_ONCE(*X); } P1(int *X, int *DYNTICKS) { int dynticks; WRITE_ONCE(*X, 1); smp_mb(); dynticks = smp_load_acquire(DYNTICKS); } exists (1:dynticks=0 /\ 0:x=1) Running "herd7 -conf linux-kernel.cfg dynticks-from-idle.litmus" verifies this transition, namely, showing that if the RCU grace-period kthread (P1) sees another CPU as idle (P0), then any memory access prior to the start of the grace period (P1's write to X) will be seen by any RCU read-side critical section following the to-non-idle transition (P0's read from X). This is a straightforward use of full memory barriers to force ordering in a store-buffering (SB) litmus test. The following litmus test, also adapted from the one supplied off-list by Frederic Weisbecker, models the RCU grace-period kthread detecting a non-idle CPU that is concurrently transitioning to idle: C dynticks-into-idle { DYNTICKS=1; (* Initially non-idle. *) } P0(int *X, int *DYNTICKS) { int dynticks; // Non-idle. WRITE_ONCE(*X, 1); dynticks = READ_ONCE(*DYNTICKS); smp_store_release(DYNTICKS, dynticks + 1); smp_mb(); // Now idle. } P1(int *X, int *DYNTICKS) { int x; int dynticks; smp_mb(); dynticks = smp_load_acquire(DYNTICKS); x = READ_ONCE(*X); } exists (1:dynticks=2 /\ 1:x=0) Running "herd7 -conf linux-kernel.cfg dynticks-into-idle.litmus" verifies this transition, namely, showing that if the RCU grace-period kthread (P1) sees another CPU as newly idle (P0), then any pre-idle memory access (P0's write to X) will be seen by any code following the grace period (P1's read from X). This is a simple release-acquire pair forcing ordering in a message-passing (MP) litmus test. Of course, if the grace-period kthread detects the CPU as non-idle, it will refrain from reporting a quiescent state on behalf of that CPU, so there are no ordering requirements from the grace-period kthread in that case. However, other subsystems call rcu_is_idle_cpu() to check for CPUs being non-idle from an RCU perspective. That case is also verified by the above litmus tests with the proviso that the sense of the low-order bit of the DYNTICKS counter be inverted. Unfortunately, on x86 smp_mb() is as expensive as a cache-local atomic increment. This commit therefore weakens only the read from ->dynticks. However, the updates are abstracted into a rcu_dynticks_inc() function to ease any future changes that might be needed. [ paulmck: Apply Linus Torvalds feedback. ] Link: https://lore.kernel.org/lkml/20210721202127.2129660-4-paulmck@kernel.org/ Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Acked-by: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Remove special bit at the bottom of the ->dynticks counterJoel Fernandes (Google)2021-08-061-63/+14
|/ | | | | | | | | | | | | | Commit b8c17e6664c4 ("rcu: Maintain special bits at bottom of ->dynticks counter") reserved a bit at the bottom of the ->dynticks counter to defer flushing of TLBs, but this facility never has been used. This commit therefore removes this capability along with the rcu_eqs_special_set() function used to trigger it. Link: https://lore.kernel.org/linux-doc/CALCETrWNPOOdTrFabTDd=H7+wc6xJ9rJceg6OL1S0rTV5pfSsA@mail.gmail.com/ Suggested-by: Andy Lutomirski <luto@kernel.org> Signed-off-by: "Joel Fernandes (Google)" <joel@joelfernandes.org> [ paulmck: Forward-port to v5.13-rc1. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
* Merge branch 'core-rcu-2021.07.04' of ↵Linus Torvalds2021-07-041-139/+174
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu Pull RCU updates from Paul McKenney: - Bitmap parsing support for "all" as an alias for all bits - Documentation updates - Miscellaneous fixes, including some that overlap into mm and lockdep - kvfree_rcu() updates - mem_dump_obj() updates, with acks from one of the slab-allocator maintainers - RCU NOCB CPU updates, including limited deoffloading - SRCU updates - Tasks-RCU updates - Torture-test updates * 'core-rcu-2021.07.04' of git://git.kernel.org/pub/scm/linux/kernel/git/paulmck/linux-rcu: (78 commits) tasks-rcu: Make show_rcu_tasks_gp_kthreads() be static inline rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent states rcu: Add missing __releases() annotation rcu: Remove obsolete rcu_read_unlock() deadlock commentary rcu: Improve comments describing RCU read-side critical sections rcu: Create an unrcu_pointer() to remove __rcu from a pointer srcu: Early test SRCU polling start rcu: Fix various typos in comments rcu/nocb: Unify timers rcu/nocb: Prepare for fine-grained deferred wakeup rcu/nocb: Only cancel nocb timer if not polling rcu/nocb: Delete bypass_timer upon nocb_gp wakeup rcu/nocb: Cancel nocb_timer upon nocb_gp wakeup rcu/nocb: Allow de-offloading rdp leader rcu/nocb: Directly call __wake_nocb_gp() from bypass timer rcu: Don't penalize priority boosting when there is nothing to boost rcu: Point to documentation of ordering guarantees rcu: Make rcu_gp_cleanup() be noinline for tracing rcu: Restrict RCU_STRICT_GRACE_PERIOD to at most four CPUs rcu: Make show_rcu_gp_kthreads() dump rcu_node structures blocking GP ...
| *-------. Merge branches 'bitmaprange.2021.05.10c', 'doc.2021.05.10c', ↵Paul E. McKenney2021-05-181-139/+174
| |\ \ \ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'fixes.2021.05.13a', 'kvfree_rcu.2021.05.10c', 'mmdumpobj.2021.05.10c', 'nocb.2021.05.12a', 'srcu.2021.05.12a', 'tasks.2021.05.18a' and 'torture.2021.05.10c' into HEAD bitmaprange.2021.05.10c: Allow "all" for bitmap ranges. doc.2021.05.10c: Documentation updates. fixes.2021.05.13a: Miscellaneous fixes. kvfree_rcu.2021.05.10c: kvfree_rcu() updates. mmdumpobj.2021.05.10c: mem_dump_obj() updates. nocb.2021.05.12a: RCU NOCB CPU updates, including limited deoffloading. srcu.2021.05.12a: SRCU updates. tasks.2021.05.18a: Tasks-RCU updates. torture.2021.05.10c: Torture-test updates.
| | | | | | * rcu-tasks: Make ksoftirqd provide RCU Tasks quiescent statesPaul E. McKenney2021-05-181-0/+1
| | |_|_|_|/ | |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Heavy networking load can cause a CPU to execute continuously and indefinitely within ksoftirqd, in which case there will be no voluntary task switches and thus no RCU-tasks quiescent states. This commit therefore causes the exiting rcu_softirq_qs() to provide an RCU-tasks quiescent state. This of course means that __do_softirq() and its callers cannot be invoked from within a tracing trampoline. Reported-by: Toke Høiland-Jørgensen <toke@redhat.com> Tested-by: Toke Høiland-Jørgensen <toke@redhat.com> Reviewed-by: Masami Hiramatsu <mhiramat@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Masami Hiramatsu <mhiramat@kernel.org>
| | | | | * srcu: Fix broken node geometry after early ssp initFrederic Weisbecker2021-05-101-1/+15
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | An srcu_struct structure that is initialized before rcu_init_geometry() will have its srcu_node hierarchy based on CONFIG_NR_CPUS. Once rcu_init_geometry() is called, this hierarchy is compressed as needed for the actual maximum number of CPUs for this system. Later on, that srcu_struct structure is confused, sometimes referring to its initial CONFIG_NR_CPUS-based hierarchy, and sometimes instead to the new num_possible_cpus() hierarchy. For example, each of its ->mynode fields continues to reference the original leaf rcu_node structures, some of which might no longer exist. On the other hand, srcu_for_each_node_breadth_first() traverses to the new node hierarchy. There are at least two bad possible outcomes to this: 1) a) A callback enqueued early on an srcu_data structure (call it *sdp) is recorded pending on sdp->mynode->srcu_data_have_cbs in srcu_funnel_gp_start() with sdp->mynode pointing to a deep leaf (say 3 levels). b) The grace period ends after rcu_init_geometry() shrinks the nodes level to a single one. srcu_gp_end() walks through the new srcu_node hierarchy without ever reaching the old leaves so the callback is never executed. This is easily reproduced on an 8 CPUs machine with CONFIG_NR_CPUS >= 32 and "rcupdate.rcu_self_test=1". The srcu_barrier() after early tests verification never completes and the boot hangs: [ 5413.141029] INFO: task swapper/0:1 blocked for more than 4915 seconds. [ 5413.147564] Not tainted 5.12.0-rc4+ #28 [ 5413.151927] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message. [ 5413.159753] task:swapper/0 state:D stack: 0 pid: 1 ppid: 0 flags:0x00004000 [ 5413.168099] Call Trace: [ 5413.170555] __schedule+0x36c/0x930 [ 5413.174057] ? wait_for_completion+0x88/0x110 [ 5413.178423] schedule+0x46/0xf0 [ 5413.181575] schedule_timeout+0x284/0x380 [ 5413.185591] ? wait_for_completion+0x88/0x110 [ 5413.189957] ? mark_held_locks+0x61/0x80 [ 5413.193882] ? mark_held_locks+0x61/0x80 [ 5413.197809] ? _raw_spin_unlock_irq+0x24/0x50 [ 5413.202173] ? wait_for_completion+0x88/0x110 [ 5413.206535] wait_for_completion+0xb4/0x110 [ 5413.210724] ? srcu_torture_stats_print+0x110/0x110 [ 5413.215610] srcu_barrier+0x187/0x200 [ 5413.219277] ? rcu_tasks_verify_self_tests+0x50/0x50 [ 5413.224244] ? rdinit_setup+0x2b/0x2b [ 5413.227907] rcu_verify_early_boot_tests+0x2d/0x40 [ 5413.232700] do_one_initcall+0x63/0x310 [ 5413.236541] ? rdinit_setup+0x2b/0x2b [ 5413.240207] ? rcu_read_lock_sched_held+0x52/0x80 [ 5413.244912] kernel_init_freeable+0x253/0x28f [ 5413.249273] ? rest_init+0x250/0x250 [ 5413.252846] kernel_init+0xa/0x110 [ 5413.256257] ret_from_fork+0x22/0x30 2) An srcu_struct structure that is initialized before rcu_init_geometry() and used afterward will always have stale rdp->mynode references, resulting in callbacks to be missed in srcu_gp_end(), just like in the previous scenario. This commit therefore causes init_srcu_struct_nodes to initialize the geometry, if needed. This ensures that the srcu_node hierarchy is properly built and distributed from the get-go. Suggested-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Uladzislau Rezki <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | | | * srcu: Initialize SRCU after timersFrederic Weisbecker2021-05-101-1/+0
| | |_|_|/ | |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Once srcu_init() is called, the SRCU core will make use of delayed workqueues, which rely on timers. However init_timers() is called several steps after rcu_init(). This means that a call_srcu() after rcu_init() but before init_timers() would find itself within a dangerously uninitialized timer core. This commit therefore creates a separate call to srcu_init() after init_timer() completes, which ensures that we stay in early SRCU mode until timers are safe(r). Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Uladzislau Rezki <urezki@gmail.com> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Joel Fernandes <joel@joelfernandes.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | | * rcu: Fix various typos in commentsIngo Molnar2021-05-121-3/+3
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Fix ~12 single-word typos in RCU code comments. [ paulmck: Apply feedback from Randy Dunlap. ] Reviewed-by: Randy Dunlap <rdunlap@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | | * rcu/nocb: Prepare for fine-grained deferred wakeupFrederic Weisbecker2021-05-121-1/+1
| | |_|/ | |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Tuning the deferred wakeup level must be done from a safe wakeup point. Currently those sites are: * ->nocb_timer * user/idle/guest entry * CPU down * softirq/rcuc All of these sites perform the wake up for both RCU_NOCB_WAKE and RCU_NOCB_WAKE_FORCE. In order to merge ->nocb_timer and ->nocb_bypass_timer together, we plan to add a new RCU_NOCB_WAKE_BYPASS that really should be deferred until a timer fires so that we don't wake up the NOCB-gp kthread too early. To prepare for that, this commit specifies the per-callsite wakeup level/limit. Cc: Josh Triplett <josh@joshtriplett.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> [ paulmck: Fix non-NOCB rcu_nocb_need_deferred_wakeup() definition. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * kvfree_rcu: Refactor kfree_rcu_monitor()Uladzislau Rezki (Sony)2021-05-101-58/+26
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently we have three functions which depend on each other. Two of them are quite tiny and the last one where the most work is done. All of them are related to queuing RCU batches to reclaim objects after a GP. 1. kfree_rcu_monitor(). It consist of few lines. It acquires a spin-lock and calls kfree_rcu_drain_unlock(). 2. kfree_rcu_drain_unlock(). It also consists of few lines of code. It calls queue_kfree_rcu_work() to queue the batch. If this fails, it rearms the monitor work to try again later. 3. queue_kfree_rcu_work(). This provides the bulk of the functionality, attempting to start a new batch to free objects after a GP. Since there are no external users of functions [2] and [3], both can eliminated by moving all logic directly into [1], which both shrinks and simplifies the code. Also replace comments which start with "/*" to "//" format to make it unified across the file. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * kvfree_rcu: Fix comments according to current codeUladzislau Rezki (Sony)2021-05-101-6/+9
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The kvfree_rcu() function now defers allocations in the common case due to the fact that there is no lockless access to the memory-allocator caches/pools. In addition, in CONFIG_PREEMPT_NONE=y and in CONFIG_PREEMPT_VOLUNTARY=y kernels, there is no reliable way to determine if spinlocks are held. As a result, allocation is deferred in the common case, and the two-argument form of kvfree_rcu() thus uses the "channel 3" queue through all the rcu_head structures. This channel is called referred to as the emergency case in comments, and these comments are now obsolete. This commit therefore updates these comments to reflect the new common-case nature of such emergencies. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * kvfree_rcu: Use kfree_rcu_monitor() instead of open-coded variantUladzislau Rezki (Sony)2021-05-101-7/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Replace an open-coded version of the kfree_rcu_monitor() function body with a call to that function. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * kvfree_rcu: Update "monitor_todo" once a batch is startedUladzislau Rezki (Sony)2021-05-101-2/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Before attempting to start a new batch the "monitor_todo" variable is set to "false" and set back to "true" when a previous RCU batch is still in progress. This is at best confusing. Thus change this variable to "false" only when a new batch has been successfully queued, otherwise, just leave it be. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * kvfree_rcu: Add a bulk-list check when a scheduler is runUladzislau Rezki (Sony)2021-05-101-1/+2
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The rcu_scheduler_active flag is set to RCU_SCHEDULER_RUNNING once the scheduler is up and running. That signal is used in order to check and queue a "monitor work" to reclaim freed objects (if there are any) during early boot. This flag is used by kvfree_rcu() to determine when work can safely be queued, at which point memory passed to earlier invocations of kvfree_rcu() can be processed. However, only "krcp->head" is checked for objects that need to be released, and there are now two more, namely, "krcp->bkvhead[0]" and "krcp->bkvhead[1]". Therefore, check these two additional channels. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * kvfree_rcu: Use [READ/WRITE]_ONCE() macros to access to nr_bkv_objsUladzislau Rezki (Sony)2021-05-101-10/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | nr_bkv_objs is a count of the objects in the kvfree_rcu page cache. Accessing it requires holding the ->lock. Switch to READ_ONCE() and WRITE_ONCE() macros to provide lockless access to this counter. This lockless access is used for the shrinker. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * kvfree_rcu: Release a page cache under memory pressureZhang Qiang2021-05-101-9/+73
| | |/ | |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Add a drain_page_cache() function to drain a per-cpu page cache. The reason behind of it is a system can run into a low memory condition, in that case a page shrinker can ask for its users to free their caches in order to get extra memory available for other needs in a system. When a system hits such condition, a page cache is drained for all CPUs in a system. By default a page cache work is delayed with 5 seconds interval until a memory pressure disappears, if needed it can be changed. See a rcu_delay_page_cache_fill_msec module parameter. Co-developed-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Zqiang <qiang.zhang@windriver.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu: Improve comments describing RCU read-side critical sectionsPaul E. McKenney2021-05-131-10/+14
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There are a number of places that call out the fact that preempt-disable regions of code now act as RCU read-side critical sections, where preempt-disable regions of code include irq-disable regions of code, bh-disable regions of code, hardirq handlers, and NMI handlers. However, someone relying solely on (for example) the call_rcu() header comment might well have no idea that preempt-disable regions of code have RCU semantics. This commit therefore updates the header comments for call_rcu(), synchronize_rcu(), rcu_dereference_bh_check(), and rcu_dereference_sched_check() to call out these new(ish) forms of RCU readers. Reported-by: Michel Lespinasse <michel@lespinasse.org> [ paulmck: Apply Matthew Wilcox and Michel Lespinasse feedback. ] Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu: Point to documentation of ordering guaranteesPaul E. McKenney2021-05-101-2/+18
| | | | | | | | | | | | | | | | | | | | | Add comments to synchronize_rcu() and friends that point to Documentation/RCU/Design/Memory-Ordering/Tree-RCU-Memory-Ordering.rst. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu: Make rcu_gp_cleanup() be noinline for tracingPaul E. McKenney2021-05-101-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | Although there are trace events for RCU grace periods, these are only enabled in CONFIG_RCU_TRACE=y kernels. This commit therefore marks rcu_gp_cleanup() noinline in order to provide a function that can be traced that is invoked near the end of each grace period. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu: Make RCU priority boosting work on single-CPU rcu_node structuresPaul E. McKenney2021-05-101-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | When any CPU comes online, it checks to see if an RCU-boost kthread has already been created for that CPU's leaf rcu_node structure, and if not, it creates one. Unfortunately, it also verifies that this leaf rcu_node structure actually has at least one online CPU, and if not, it declines to create the kthread. Although this behavior makes sense during early boot, especially on systems that claim far more CPUs than they actually have, it makes no sense for the first CPU to come online for a given rcu_node structure. There is no point in checking because we know there is a CPU on its way in. The problem is that timing differences can cause this incoming CPU to not yet be reflected in the various bit masks even at rcutree_online_cpu() time, and there is no chance at rcutree_prepare_cpu() time. Plus it would be better to create the RCU-boost kthread at rcutree_prepare_cpu() to handle the case where the CPU is involved in an RCU priority inversion very shortly after it comes online. This commit therefore moves the checking to rcu_prepare_kthreads(), which is called only at early boot, when the check is appropriate. In addition, it makes rcutree_prepare_cpu() invoke rcu_spawn_one_boost_kthread(), which no longer does any checking for online CPUs. With this change, RCU priority boosting tests now pass for short rcutorture runs, even with single-CPU leaf rcu_node structures. Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: Scott Wood <swood@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu: Invoke rcu_spawn_core_kthreads() from rcu_spawn_gp_kthread()Paul E. McKenney2021-05-101-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Currently, rcu_spawn_core_kthreads() is invoked via an early_initcall(), which works, except that rcu_spawn_gp_kthread() is also invoked via an early_initcall() and rcu_spawn_core_kthreads() relies on adjustments to kthread_prio that are carried out by rcu_spawn_gp_kthread(). There is no guaranttee of ordering among early_initcall() handlers, and thus no guarantee that kthread_prio will be properly checked and range-limited at the time that rcu_spawn_core_kthreads() needs it. In most cases, this bug is harmless. After all, the only reason that rcu_spawn_gp_kthread() adjusts the value of kthread_prio is if the user specified a nonsensical value for this boot parameter, which experience indicates is rare. Nevertheless, a bug is a bug. This commit therefore causes the rcu_spawn_core_kthreads() function to be invoked directly from rcu_spawn_gp_kthread() after any needed adjustments to kthread_prio have been carried out. Fixes: 48d07c04b4cc ("rcu: Enable elimination of Tree-RCU softirq processing") Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu: Improve tree.c comments and add code cleanupsZhouyi Zhou2021-05-101-12/+12
| | | | | | | | | | | | | | | | | | | | | This commit cleans up some comments and code in kernel/rcu/tree.c. Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * rcu: Remove the unused rcu_irq_exit_preempt() functionPaul E. McKenney2021-05-101-22/+0
| |/ | | | | | | | | | | | | | | | | | | Commit 9ee01e0f69a9 ("x86/entry: Clean up idtentry_enter/exit() leftovers") left the rcu_irq_exit_preempt() in place in order to avoid conflicts with the -rcu tree. Now that this change has long since hit mainline, this commit removes the no-longer-used rcu_irq_exit_preempt() function. Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
* / kernel.h: split out panic and oops helpersAndy Shevchenko2021-07-011-0/+2
|/ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | kernel.h is being used as a dump for all kinds of stuff for a long time. Here is the attempt to start cleaning it up by splitting out panic and oops helpers. There are several purposes of doing this: - dropping dependency in bug.h - dropping a loop by moving out panic_notifier.h - unload kernel.h from something which has its own domain At the same time convert users tree-wide to use new headers, although for the time being include new header back to kernel.h to avoid twisted indirected includes for existing users. [akpm@linux-foundation.org: thread_info.h needs limits.h] [andriy.shevchenko@linux.intel.com: ia64 fix] Link: https://lkml.kernel.org/r/20210520130557.55277-1-andriy.shevchenko@linux.intel.com Link: https://lkml.kernel.org/r/20210511074137.33666-1-andriy.shevchenko@linux.intel.com Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com> Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org> Co-developed-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Mike Rapoport <rppt@linux.ibm.com> Acked-by: Corey Minyard <cminyard@mvista.com> Acked-by: Christian Brauner <christian.brauner@ubuntu.com> Acked-by: Arnd Bergmann <arnd@arndb.de> Acked-by: Kees Cook <keescook@chromium.org> Acked-by: Wei Liu <wei.liu@kernel.org> Acked-by: Rasmus Villemoes <linux@rasmusvillemoes.dk> Signed-off-by: Andrew Morton <akpm@linux-foundation.org> Acked-by: Sebastian Reichel <sre@kernel.org> Acked-by: Luis Chamberlain <mcgrof@kernel.org> Acked-by: Stephen Boyd <sboyd@kernel.org> Acked-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de> Acked-by: Helge Deller <deller@gmx.de> # parisc Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
*-----. Merge branches 'bitmaprange.2021.03.08a', 'fixes.2021.03.15a', ↵Paul E. McKenney2021-03-241-45/+124
|\ \ \ \ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | 'kvfree_rcu.2021.03.08a', 'mmdumpobj.2021.03.08a', 'nocb.2021.03.15a', 'poll.2021.03.24a', 'rt.2021.03.08a', 'tasks.2021.03.08a', 'torture.2021.03.08a' and 'torturescript.2021.03.22a' into HEAD bitmaprange.2021.03.08a: Allow 3-N for bitmap ranges. fixes.2021.03.15a: Miscellaneous fixes. kvfree_rcu.2021.03.08a: kvfree_rcu() updates. mmdumpobj.2021.03.08a: mem_dump_obj() updates. nocb.2021.03.15a: RCU NOCB CPU updates, including limited deoffloading. poll.2021.03.24a: Polling grace-period interfaces for RCU. rt.2021.03.08a: Realtime-related RCU changes. tasks.2021.03.08a: Tasks-RCU updates. torture.2021.03.08a: Torture-test updates. torturescript.2021.03.22a: Torture-test scripting updates.
| | | | * rcu: Provide polling interfaces for Tree RCU grace periodsPaul E. McKenney2021-03-221-7/+68
| |_|_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | There is a need for a non-blocking polling interface for RCU grace periods, so this commit supplies start_poll_synchronize_rcu() and poll_state_synchronize_rcu() for this purpose. Note that the existing get_state_synchronize_rcu() may be used if future grace periods are inevitable (perhaps due to a later call_rcu() invocation). The new start_poll_synchronize_rcu() is to be used if future grace periods might not otherwise happen. Finally, poll_state_synchronize_rcu() provides a lockless check for a grace period having elapsed since the corresponding call to either of the get_state_synchronize_rcu() or start_poll_synchronize_rcu(). As with get_state_synchronize_rcu(), the return value from either get_state_synchronize_rcu() or start_poll_synchronize_rcu() is passed in to a later call to either poll_state_synchronize_rcu() or the existing (might_sleep) cond_synchronize_rcu(). [ paulmck: Remove redundant smp_mb() per Frederic Weisbecker feedback. ] [ Update poll_state_synchronize_rcu() docbook per Frederic Weisbecker feedback. ] Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * rcu/nocb: Only (re-)initialize segcblist when needed on CPU upFrederic Weisbecker2021-03-081-5/+4
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | At the start of a CPU-hotplug operation, the incoming CPU's callback list can be in a number of states: 1. Disabled and empty. This is the case when the boot CPU has not invoked call_rcu(), when a non-boot CPU first comes online, and when a non-offloaded CPU comes back online. In this case, it is both necessary and permissible to initialize ->cblist. Because either the CPU is currently running with interrupts disabled (boot CPU) or is not yet running at all (other CPUs), it is not necessary to acquire ->nocb_lock. In this case, initialization is required. 2. Disabled and non-empty. This cannot occur, because early boot call_rcu() invocations enable the callback list before enqueuing their callback. 3. Enabled, whether empty or not. In this case, the callback list has already been initialized. This case occurs when the boot CPU has executed an early boot call_rcu() and also when an offloaded CPU comes back online. In both cases, there is no need to initialize the callback list: In the boot-CPU case, the CPU has not (yet) gone offline, and in the offloaded case, the rcuo kthreads are taking care of business. Because it is not necessary to initialize the callback list, it is also not necessary to acquire ->nocb_lock. Therefore, checking if the segcblist is enabled suffices. This commit therefore initializes the callback list at rcutree_prepare_cpu() time only if that list is disabled. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * rcu/nocb: Forbid NOCB toggling on offline CPUsFrederic Weisbecker2021-03-081-2/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | It makes no sense to de-offload an offline CPU because that CPU will never invoke any remaining callbacks. It also makes little sense to offload an offline CPU because any pending RCU callbacks were migrated when that CPU went offline. Yes, it is in theory possible to use a number of tricks to permit offloading and deoffloading offline CPUs in certain cases, but in practice it is far better to have the simple and deterministic rule "Toggling the offload state of an offline CPU is forbidden". For but one example, consider that an offloaded offline CPU might have millions of callbacks queued. Best to just say "no". This commit therefore forbids toggling of the offloaded state of offline CPUs. Reported-by: Paul E. McKenney <paulmck@kernel.org> Cc: Josh Triplett <josh@joshtriplett.org> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | | * rcu/nocb: Detect unsafe checks for offloaded rdpFrederic Weisbecker2021-03-081-10/+11
| |_|/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Provide CONFIG_PROVE_RCU sanity checks to ensure we are always reading the offloaded state of an rdp in a safe and stable way and prevent from its value to be changed under us. We must either hold the barrier mutex, the cpu-hotplug lock (read or write) or the nocb lock. Local non-preemptible reads are also safe. NOCB kthreads and timers have their own means of synchronization against the offloaded state updaters. Cc: Josh Triplett <josh@joshtriplett.org> Cc: Steven Rostedt <rostedt@goodmis.org> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> Cc: Lai Jiangshan <jiangshanlai@gmail.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Neeraj Upadhyay <neeraju@codeaurora.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Boqun Feng <boqun.feng@gmail.com> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * kvfree_rcu: Use same set of GFP flags as does single-argumentUladzislau Rezki (Sony)2021-03-081-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Running an rcuscale stress-suite can lead to "Out of memory" of a system. This can happen under high memory pressure with a small amount of physical memory. For example, a KVM test configuration with 64 CPUs and 512 megabytes can result in OOM when running rcuscale with below parameters: ../kvm.sh --torture rcuscale --allcpus --duration 10 --kconfig CONFIG_NR_CPUS=64 \ --bootargs "rcuscale.kfree_rcu_test=1 rcuscale.kfree_nthreads=16 rcuscale.holdoff=20 \ rcuscale.kfree_loops=10000 torture.disable_onoff_at_boot" --trust-make <snip> [ 12.054448] kworker/1:1H invoked oom-killer: gfp_mask=0x2cc0(GFP_KERNEL|__GFP_NOWARN), order=0, oom_score_adj=0 [ 12.055303] CPU: 1 PID: 377 Comm: kworker/1:1H Not tainted 5.11.0-rc3+ #510 [ 12.055416] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-1 04/01/2014 [ 12.056485] Workqueue: events_highpri fill_page_cache_func [ 12.056485] Call Trace: [ 12.056485] dump_stack+0x57/0x6a [ 12.056485] dump_header+0x4c/0x30a [ 12.056485] ? del_timer_sync+0x20/0x30 [ 12.056485] out_of_memory.cold.47+0xa/0x7e [ 12.056485] __alloc_pages_slowpath.constprop.123+0x82f/0xc00 [ 12.056485] __alloc_pages_nodemask+0x289/0x2c0 [ 12.056485] __get_free_pages+0x8/0x30 [ 12.056485] fill_page_cache_func+0x39/0xb0 [ 12.056485] process_one_work+0x1ed/0x3b0 [ 12.056485] ? process_one_work+0x3b0/0x3b0 [ 12.060485] worker_thread+0x28/0x3c0 [ 12.060485] ? process_one_work+0x3b0/0x3b0 [ 12.060485] kthread+0x138/0x160 [ 12.060485] ? kthread_park+0x80/0x80 [ 12.060485] ret_from_fork+0x22/0x30 [ 12.062156] Mem-Info: [ 12.062350] active_anon:0 inactive_anon:0 isolated_anon:0 [ 12.062350] active_file:0 inactive_file:0 isolated_file:0 [ 12.062350] unevictable:0 dirty:0 writeback:0 [ 12.062350] slab_reclaimable:2797 slab_unreclaimable:80920 [ 12.062350] mapped:1 shmem:2 pagetables:8 bounce:0 [ 12.062350] free:10488 free_pcp:1227 free_cma:0 ... [ 12.101610] Out of memory and no killable processes... [ 12.102042] Kernel panic - not syncing: System is deadlocked on memory [ 12.102583] CPU: 1 PID: 377 Comm: kworker/1:1H Not tainted 5.11.0-rc3+ #510 [ 12.102600] Hardware name: QEMU Standard PC (Q35 + ICH9, 2009), BIOS 1.12.0-1 04/01/2014 <snip> Because kvfree_rcu() has a fallback path, memory allocation failure is not the end of the world. Furthermore, the added overhead of aggressive GFP settings must be balanced against the overhead of the fallback path, which is a cache miss for double-argument kvfree_rcu() and a call to synchronize_rcu() for single-argument kvfree_rcu(). The current choice of GFP_KERNEL|__GFP_NOWARN can result in longer latencies than a call to synchronize_rcu(), so less-tenacious GFP flags would be helpful. Here is the tradeoff that must be balanced: a) Minimize use of the fallback path, b) Avoid pushing the system into OOM, c) Bound allocation latency to that of synchronize_rcu(), and d) Leave the emergency reserves to use cases lacking fallbacks. This commit therefore changes GFP flags from GFP_KERNEL|__GFP_NOWARN to GFP_KERNEL|__GFP_NORETRY|__GFP_NOMEMALLOC|__GFP_NOWARN. This combination leaves the emergency reserves alone and can initiate reclaim, but will not invoke the OOM killer. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * kvfree_rcu: Replace __GFP_RETRY_MAYFAIL by __GFP_NORETRYUladzislau Rezki (Sony)2021-03-081-1/+13
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | __GFP_RETRY_MAYFAIL can spend quite a bit of time reclaiming, and this can be wasted effort given that there is a fallback code path in case memory allocation fails. __GFP_NORETRY does perform some light-weight reclaim, but it will fail under OOM conditions, allowing the fallback to be taken as an alternative to hard-OOMing the system. There is a four-way tradeoff that must be balanced: 1) Minimize use of the fallback path; 2) Avoid full-up OOM; 3) Do a light-wait allocation request; 4) Avoid dipping into the emergency reserves. Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Acked-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * kvfree_rcu: Make krc_this_cpu_unlock() use raw_spin_unlock_irqrestore()Paul E. McKenney2021-03-081-2/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | The krc_this_cpu_unlock() function does a raw_spin_unlock() immediately followed by a local_irq_restore(). This commit saves a line of code by merging them into a raw_spin_unlock_irqrestore(). This transformation also reduces scheduling latency because raw_spin_unlock_irqrestore() responds immediately to a reschedule request. In contrast, local_irq_restore() does a scheduling-oblivious enabling of interrupts. Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * kvfree_rcu: Use __GFP_NOMEMALLOC for single-argument kvfree_rcu()Paul E. McKenney2021-03-081-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | This commit applies the __GFP_NOMEMALLOC gfp flag to memory allocations carried out by the single-argument variant of kvfree_rcu(), thus avoiding this can-sleep code path from dipping into the emergency reserves. Acked-by: Michal Hocko <mhocko@suse.com> Suggested-by: Michal Hocko <mhocko@suse.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| | * kvfree_rcu: Directly allocate page for single-argument caseUladzislau Rezki (Sony)2021-03-081-16/+26
| |/ |/| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Single-argument kvfree_rcu() must be invoked from sleepable contexts, so we can directly allocate pages. Furthermmore, the fallback in case of page-allocation failure is the high-latency synchronize_rcu(), so it makes sense to do these page allocations from the fastpath, and even to permit limited sleeping within the allocator. This commit therefore allocates if needed on the fastpath using GFP_KERNEL|__GFP_RETRY_MAYFAIL. This also has the beneficial effect of leaving kvfree_rcu()'s per-CPU caches to the double-argument variant of kvfree_rcu(), given that the double-argument variant cannot directly invoke the allocator. [ paulmck: Add add_ptr_to_bulk_krc_lock header comment per Michal Hocko. ] Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Remove spurious instrumentation_end() in rcu_nmi_enter()Zhouyi Zhou2021-03-081-1/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | In rcu_nmi_enter(), there is an erroneous instrumentation_end() in the second branch of the "if" statement. Oddly enough, "objtool check -f vmlinux.o" fails to complain because it is unable to correctly cover all cases. Instead, objtool visits the third branch first, which marks following trace_rcu_dyntick() as visited. This commit therefore removes the spurious instrumentation_end(). Fixes: 04b25a495bd6 ("rcu: Mark rcu_nmi_enter() call to rcu_cleanup_after_idle() noinstr") Reported-by Neeraj Upadhyay <neeraju@codeaurora.org> Signed-off-by: Zhouyi Zhou <zhouzhouyi@gmail.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Fix CPU-offline trace in rcutree_dying_cpuNeeraj Upadhyay2021-03-081-1/+1
| | | | | | | | | | | | | | | | | | | | | | | | The condition in the trace_rcu_grace_period() in rcutree_dying_cpu() is backwards, so that it uses the string "cpuofl" when the offline CPU is blocking the current grace period and "cpuofl-bgp" otherwise. Given that the "-bgp" stands for "blocking grace period", this is at best misleading. This commit therefore switches these strings in order to correctly trace whether the outgoing cpu blocks the current grace period. Signed-off-by: Neeraj Upadhyay <neeraju@codeaurora.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
| * rcu: Remove superfluous rdp fetchFrederic Weisbecker2021-03-081-1/+0
|/ | | | | | | | | Cc: Rafael J. Wysocki <rafael.j.wysocki@intel.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Ingo Molnar<mingo@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
* Merge tag 'sched-core-2021-02-17' of ↵Linus Torvalds2021-02-211-1/+52
|\ | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip Pull scheduler updates from Ingo Molnar: "Core scheduler updates: - Add CONFIG_PREEMPT_DYNAMIC: this in its current form adds the preempt=none/voluntary/full boot options (default: full), to allow distros to build a PREEMPT kernel but fall back to close to PREEMPT_VOLUNTARY (or PREEMPT_NONE) runtime scheduling behavior via a boot time selection. There's also the /debug/sched_debug switch to do this runtime. This feature is implemented via runtime patching (a new variant of static calls). The scope of the runtime patching can be best reviewed by looking at the sched_dynamic_update() function in kernel/sched/core.c. ( Note that the dynamic none/voluntary mode isn't 100% identical, for example preempt-RCU is available in all cases, plus the preempt count is maintained in all models, which has runtime overhead even with the code patching. ) The PREEMPT_VOLUNTARY/PREEMPT_NONE models, used by the vast majority of distributions, are supposed to be unaffected. - Fix ignored rescheduling after rcu_eqs_enter(). This is a bug that was found via rcutorture triggering a hang. The bug is that rcu_idle_enter() may wake up a NOCB kthread, but this happens after the last generic need_resched() check. Some cpuidle drivers fix it by chance but many others don't. In true 2020 fashion the original bug fix has grown into a 5-patch scheduler/RCU fix series plus another 16 RCU patches to address the underlying issue of missed preemption events. These are the initial fixes that should fix current incarnations of the bug. - Clean up rbtree usage in the scheduler, by providing & using the following consistent set of rbtree APIs: partial-order; less() based: - rb_add(): add a new entry to the rbtree - rb_add_cached(): like rb_add(), but for a rb_root_cached total-order; cmp() based: - rb_find(): find an entry in an rbtree - rb_find_add(): find an entry, and add if not found - rb_find_first(): find the first (leftmost) matching entry - rb_next_match(): continue from rb_find_first() - rb_for_each(): iterate a sub-tree using the previous two - Improve the SMP/NUMA load-balancer: scan for an idle sibling in a single pass. This is a 4-commit series where each commit improves one aspect of the idle sibling scan logic. - Improve the cpufreq cooling driver by getting the effective CPU utilization metrics from the scheduler - Improve the fair scheduler's active load-balancing logic by reducing the number of active LB attempts & lengthen the load-balancing interval. This improves stress-ng mmapfork performance. - Fix CFS's estimated utilization (util_est) calculation bug that can result in too high utilization values Misc updates & fixes: - Fix the HRTICK reprogramming & optimization feature - Fix SCHED_SOFTIRQ raising race & warning in the CPU offlining code - Reduce dl_add_task_root_domain() overhead - Fix uprobes refcount bug - Process pending softirqs in flush_smp_call_function_from_idle() - Clean up task priority related defines, remove *USER_*PRIO and USER_PRIO() - Simplify the sched_init_numa() deduplication sort - Documentation updates - Fix EAS bug in update_misfit_status(), which degraded the quality of energy-balancing - Smaller cleanups" * tag 'sched-core-2021-02-17' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: (51 commits) sched,x86: Allow !PREEMPT_DYNAMIC entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling point entry: Explicitly flush pending rcuog wakeup before last rescheduling point rcu/nocb: Trigger self-IPI on late deferred wake up before user resume rcu/nocb: Perform deferred wake up before last idle's need_resched() check rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callers sched/features: Distinguish between NORMAL and DEADLINE hrtick sched/features: Fix hrtick reprogramming sched/deadline: Reduce rq lock contention in dl_add_task_root_domain() uprobes: (Re)add missing get_uprobe() in __find_uprobe() smp: Process pending softirqs in flush_smp_call_function_from_idle() sched: Harden PREEMPT_DYNAMIC static_call: Allow module use without exposing static_call_key sched: Add /debug/sched_preempt preempt/dynamic: Support dynamic preempt with preempt= boot option preempt/dynamic: Provide irqentry_exit_cond_resched() static call preempt/dynamic: Provide preempt_schedule[_notrace]() static calls preempt/dynamic: Provide cond_resched() and might_resched() static calls preempt: Introduce CONFIG_PREEMPT_DYNAMIC static_call: Provide DEFINE_STATIC_CALL_RET0() ...
| * entry/kvm: Explicitly flush pending rcuog wakeup before last rescheduling pointFrederic Weisbecker2021-02-171-10/+34
| | | | | | | | | | | | | | | | | | | | | | | | | | | | Following the idle loop model, cleanly check for pending rcuog wakeup before the last rescheduling point upon resuming to guest mode. This way we can avoid to do it from rcu_user_enter() with the last resort self-IPI hack that enforces rescheduling. Suggested-by: Peter Zijlstra <peterz@infradead.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-6-frederic@kernel.org
| * entry: Explicitly flush pending rcuog wakeup before last rescheduling pointFrederic Weisbecker2021-02-171-5/+7
| | | | | | | | | | | | | | | | | | | | | | | | | | Following the idle loop model, cleanly check for pending rcuog wakeup before the last rescheduling point on resuming to user mode. This way we can avoid to do it from rcu_user_enter() with the last resort self-IPI hack that enforces rescheduling. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-5-frederic@kernel.org
| * rcu/nocb: Trigger self-IPI on late deferred wake up before user resumeFrederic Weisbecker2021-02-171-1/+20
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP kthread (rcuog) to be serviced. Unfortunately the call to rcu_user_enter() is already past the last rescheduling opportunity before we resume to userspace or to guest mode. We may escape there with the woken task ignored. The ultimate resort to fix every callsites is to trigger a self-IPI (nohz_full depends on arch to implement arch_irq_work_raise()) that will trigger a reschedule on IRQ tail or guest exit. Eventually every site that want a saner treatment will need to carefully place a call to rcu_nocb_flush_deferred_wakeup() before the last explicit need_resched() check upon resume. Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf) Reported-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-4-frederic@kernel.org
| * rcu/nocb: Perform deferred wake up before last idle's need_resched() checkFrederic Weisbecker2021-02-171-3/+0
| | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | | Entering RCU idle mode may cause a deferred wake up of an RCU NOCB_GP kthread (rcuog) to be serviced. Usually a local wake up happening while running the idle task is handled in one of the need_resched() checks carefully placed within the idle loop that can break to the scheduler. Unfortunately the call to rcu_idle_enter() is already beyond the last generic need_resched() check and we may halt the CPU with a resched request unhandled, leaving the task hanging. Fix this with splitting the rcuog wakeup handling from rcu_idle_enter() and place it before the last generic need_resched() check in the idle loop. It is then assumed that no call to call_rcu() will be performed after that in the idle loop until the CPU is put in low power mode. Fixes: 96d3fd0d315a (rcu: Break call_rcu() deadlock involving scheduler and perf) Reported-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-3-frederic@kernel.org
| * rcu: Pull deferred rcuog wake up to rcu_eqs_enter() callersFrederic Weisbecker2021-02-171-1/+10
| | | | | | | | | | | | | | | | | | | | | | | | Deferred wakeup of rcuog kthreads upon RCU idle mode entry is going to be handled differently whether initiated by idle, user or guest. Prepare with pulling that control up to rcu_eqs_enter() callers. Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Signed-off-by: Ingo Molnar <mingo@kernel.org> Cc: stable@vger.kernel.org Link: https://lkml.kernel.org/r/20210131230548.32970-2-frederic@kernel.org
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