Messages in this thread | | | Date | Mon, 24 Apr 2017 11:04:42 +0200 | From | Peter Zijlstra <> | Subject | Re: [tip:smp/hotplug] perf: Cure hotplug lock ordering issues |
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On Sun, Apr 23, 2017 at 10:16:34AM -0700, tip-bot for Thomas Gleixner wrote: > Commit-ID: 14aff62ede39a7b069beb7b95c1d02edb8ee912d > Gitweb: http://git.kernel.org/tip/14aff62ede39a7b069beb7b95c1d02edb8ee912d > Author: Thomas Gleixner <tglx@linutronix.de> > AuthorDate: Sun, 23 Apr 2017 12:13:09 +0200 > Committer: Thomas Gleixner <tglx@linutronix.de> > CommitDate: Sun, 23 Apr 2017 19:11:27 +0200 > > perf: Cure hotplug lock ordering issues > > The get_online_cpus() rework unearthed lock ordering issues. > > Reorder hotpluglock and perf_sched_mutex() to avoid circular locking > dependencies and convert static_branch_disable() to the cpuslocked version > to avoid hotplug lock recursion. > > Signed-off-by: Thomas Gleixner <tglx@linutronix.de> > Cc: Peter Zijlstra <peterz@infradead.org> > --- > kernel/events/core.c | 4 +++- > 1 file changed, 3 insertions(+), 1 deletion(-) > > diff --git a/kernel/events/core.c b/kernel/events/core.c > index 8aa3063..b5b4f52f 100644 > --- a/kernel/events/core.c > +++ b/kernel/events/core.c > @@ -4016,10 +4016,12 @@ static void unaccount_event(struct perf_event *event) > > static void perf_sched_delayed(struct work_struct *work) > { > + get_online_cpus(); > mutex_lock(&perf_sched_mutex); > if (atomic_dec_and_test(&perf_sched_count)) > - static_branch_disable(&perf_sched_events); > + static_branch_disable_cpuslocked(&perf_sched_events); > mutex_unlock(&perf_sched_mutex); > + put_online_cpus(); > }
So I think we can simply remove the perf_sched_mutex here. Its only purpose is to serialize the 0->1 state, such that nobody passes before we've done the additional sync_sched() call.
Once we're >=1, it really doesn't matter anymore. Not sure why I put it in here. Maybe extensive paranoia..
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