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Date: Tue, 15 Jul 2014 11:31:08 +0200 From: Jiri Olsa <jolsa@...hat.com> To: Peter Zijlstra <peterz@...radead.org> Cc: Jiri Olsa <jolsa@...nel.org>, linux-kernel@...r.kernel.org, Alexander Yarygin <yarygin@...ux.vnet.ibm.com>, Arnaldo Carvalho de Melo <acme@...nel.org>, Corey Ashford <cjashfor@...ux.vnet.ibm.com>, Frederic Weisbecker <fweisbec@...il.com>, Ingo Molnar <mingo@...nel.org>, Paul Mackerras <paulus@...ba.org> Subject: Re: [PATCH 2/5] perf: Destroy event's children on task exit On Tue, Jul 15, 2014 at 11:11:04AM +0200, Peter Zijlstra wrote: > On Mon, Jul 14, 2014 at 10:18:54PM +0200, Jiri Olsa wrote: > > On Mon, Jul 14, 2014 at 01:18:33PM +0200, Peter Zijlstra wrote: > > > On Fri, Jul 11, 2014 at 01:56:19PM +0200, Jiri Olsa wrote: > > > > From: Jiri Olsa <jolsa@...hat.com> SNIP > > > > I don't think this is correct, perf_event_init_context() can come in > > > concurrently and the first place it runs into ->child_mutex is after its > > > already allocated and created the (first) child event. > > > > just noticed this.. I'm working on the other version we decide, but FWIW > > there's also mutex_lock(&child_ctx->mutex); before removing the context, > > that should protect it against perf_event_init_context call > > Oh, more fail :-) > > You have: > > perf_event::child_mutex > perf_event_context::mutex > > The existing code has: > > perf_event_context::mutex > perf_event::child_context > > See for example: > > perf_event_init_context() > mutex_lock(&parent_ctx->mutex) > inherit_task_group() > inherit_group() > inherit_event() > mutex_lock(&parent_event->child_mutex) > > and > > perf_event_for_each() > mutex_lock(&ctx->mutex) > perf_event_for_each_child() > mutex_lock(&event->child_mutex) > > So the patch creates an AB-BA deadlock. ouch, right.. I'll try to come with other way thanks, jirka -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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