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authorPeter Zijlstra <peterz@infradead.org>2017-02-16 10:28:37 +0100
committerIngo Molnar <mingo@kernel.org>2017-02-24 08:56:32 +0100
commit279b5165ffadf57e2596e0ad438cb9b69b76f320 (patch)
treed89f2bdaa0ea6f610906260a348f03e2922b8032 /kernel
parent8a5897fec98e1f1fa045ccad87817eeb24579953 (diff)
downloadlinux-279b5165ffadf57e2596e0ad438cb9b69b76f320.tar.gz
perf/core: Remove confusing comment and move put_ctx()
Since commit: 321027c1fe77 ("perf/core: Fix concurrent sys_perf_event_open() vs. 'move_group' race") ... the code looks like (assuming move_group==1): gctx = __perf_event_ctx_lock_double(group_leader, ctx); perf_remove_from_context(group_leader, 0); list_for_each_entry(sibling, &group_leader->sibling_list, group_entry) { perf_remove_from_context(sibling, 0); put_ctx(gctx); } /* ... */ /* misleading comment about how this is the last reference */ put_ctx(gctx); perf_event_ctx_unlock(group_leader, gctx); What that 'last' put_ctx() does is drop @group_leader's reference on gctx after having dropped all its potential sibling references. But the thing is that __perf_event_ctx_lock_double() returns with a reference _and_ a held lock, and perf_event_ctx_unlock() unlocks that lock and drops that reference. Therefore that put_ctx() cannot be the 'last' of anything, nor is there an unbalance in puts. To reduce confusion, remove the comment and place the put_ctx() next to the remove_from_context() call. Reported-by: Ben Hutchings <ben@decadent.org.uk> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com> Cc: Arnaldo Carvalho de Melo <acme@redhat.com> Cc: Jiri Olsa <jolsa@redhat.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Stephane Eranian <eranian@google.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Vince Weaver <vincent.weaver@maine.edu> Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/events/core.c8
1 files changed, 1 insertions, 7 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c
index 77a932b..94d7b9a 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -9955,6 +9955,7 @@ SYSCALL_DEFINE5(perf_event_open,
* of swizzling perf_event::ctx.
*/
perf_remove_from_context(group_leader, 0);
+ put_ctx(gctx);
list_for_each_entry(sibling, &group_leader->sibling_list,
group_entry) {
@@ -9993,13 +9994,6 @@ SYSCALL_DEFINE5(perf_event_open,
perf_event__state_init(group_leader);
perf_install_in_context(ctx, group_leader, group_leader->cpu);
get_ctx(ctx);
-
- /*
- * Now that all events are installed in @ctx, nothing
- * references @gctx anymore, so drop the last reference we have
- * on it.
- */
- put_ctx(gctx);
}
/*