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| author | Peter Zijlstra <peterz@infradead.org> | 2017-02-16 10:28:37 +0100 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2017-02-24 08:56:32 +0100 |
| commit | 279b5165ffadf57e2596e0ad438cb9b69b76f320 (patch) | |
| tree | d89f2bdaa0ea6f610906260a348f03e2922b8032 | |
| parent | 8a5897fec98e1f1fa045ccad87817eeb24579953 (diff) | |
| download | linux-279b5165ffadf57e2596e0ad438cb9b69b76f320.tar.gz linux-279b5165ffadf57e2596e0ad438cb9b69b76f320.tar.xz | |
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>
| -rw-r--r-- | kernel/events/core.c | 8 |
1 files changed, 1 insertions, 7 deletions
diff --git a/kernel/events/core.c b/kernel/events/core.c index 77a932b54a64..94d7b9aae925 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); } /* |