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Date: Wed, 30 Dec 2009 16:08:04 +0100 From: Peter Zijlstra <peterz@...radead.org> To: Wang Liming <liming.wang@...driver.com> Cc: Ingo Molnar <mingo@...e.hu>, Frederic Weisbecker <fweisbec@...il.com>, Paul Mackerras <paulus@...ba.org>, Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org Subject: Re: [PATCH 1/1] perf_event: add check for group_list if the parent isn't counted On Wed, 2009-12-30 at 22:36 +0800, Wang Liming wrote: > > Best I can make of it is that there is a race where the parent gets his > > context instantiated and we manage to get the mutex before the other > > thread manages to add the first event. > > > > Then we observe parent_event_ctx but have an empty list. > > > > Is that it? > I didn't find this case. > In my case, if I perf record a existing process with "--pid" and finish record, > and if later the recorded process forks a process, the condition will occur. Ah, right, that will lead to the same state, since closing the last counter will not remove the context. Does the below also fix your issue? --- Subject: perf: Fix NULL deref in inheritance code From: Peter Zijlstra <a.p.zijlstra@...llo.nl> Date: Wed Dec 30 16:00:35 CET 2009 Liming found a NULL deref when a task has a perf context but no counters when it forks. This can occur in two cases, a race during construction where the fork hits after installing the context but before the first counter gets inserted, or more reproducably, a fork after the last counter is closed (which leaves the context around). CC: stable@...nel.org Reported-by: Wang Liming <liming.wang@...driver.com> Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl> --- kernel/perf_event.c | 5 ++--- 1 file changed, 2 insertions(+), 3 deletions(-) Index: linux-2.6/kernel/perf_event.c =================================================================== --- linux-2.6.orig/kernel/perf_event.c +++ linux-2.6/kernel/perf_event.c @@ -5149,7 +5149,7 @@ int perf_event_init_task(struct task_str GFP_KERNEL); if (!child_ctx) { ret = -ENOMEM; - goto exit; + break; } __perf_event_init_context(child_ctx, child); @@ -5165,7 +5165,7 @@ int perf_event_init_task(struct task_str } } - if (inherited_all) { + if (child_ctx && inherited_all) { /* * Mark the child context as a clone of the parent * context, or of whatever the parent is a clone of. @@ -5185,7 +5185,6 @@ int perf_event_init_task(struct task_str get_ctx(child_ctx->parent_ctx); } -exit: mutex_unlock(&parent_ctx->mutex); perf_unpin_context(parent_ctx); -- 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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