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| author | Andy Lutomirski <luto@kernel.org> | 2017-03-16 22:59:40 +0300 |
|---|---|---|
| committer | Ingo Molnar <mingo@kernel.org> | 2017-03-17 10:28:26 +0300 |
| commit | 4b07372a32c0c1505a7634ad7e607d83340ef645 (patch) | |
| tree | 3af5756c3cfe90f9f994356941b5435312168f70 | |
| parent | 5dc855d44c2ad960a86f593c60461f1ae1566b6d (diff) | |
| download | linux-4b07372a32c0c1505a7634ad7e607d83340ef645.tar.xz | |
x86/perf: Clarify why x86_pmu_event_mapped() isn't racy
Naively, it looks racy, but ->mmap_sem saves it. Add a comment and a
lockdep assertion.
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Cc: Arnaldo Carvalho de Melo <acme@redhat.com>
Cc: Borislav Petkov <bpetkov@suse.de>
Cc: H. Peter Anvin <hpa@zytor.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>
Link: http://lkml.kernel.org/r/03a1e629063899168dfc4707f3bb6e581e21f5c6.1489694270.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>
| -rw-r--r-- | arch/x86/events/core.c | 12 |
1 files changed, 12 insertions, 0 deletions
diff --git a/arch/x86/events/core.c b/arch/x86/events/core.c index e07b36c5588a..183a972f9210 100644 --- a/arch/x86/events/core.c +++ b/arch/x86/events/core.c @@ -2109,6 +2109,18 @@ static void x86_pmu_event_mapped(struct perf_event *event) if (!(event->hw.flags & PERF_X86_EVENT_RDPMC_ALLOWED)) return; + /* + * This function relies on not being called concurrently in two + * tasks in the same mm. Otherwise one task could observe + * perf_rdpmc_allowed > 1 and return all the way back to + * userspace with CR4.PCE clear while another task is still + * doing on_each_cpu_mask() to propagate CR4.PCE. + * + * For now, this can't happen because all callers hold mmap_sem + * for write. If this changes, we'll need a different solution. + */ + lockdep_assert_held_exclusive(¤t->mm->mmap_sem); + if (atomic_inc_return(¤t->mm->context.perf_rdpmc_allowed) == 1) on_each_cpu_mask(mm_cpumask(current->mm), refresh_pce, NULL, 1); } |