Messages in this thread Patch in this message | | | Subject | Re: [PATCH 1/1] perf_event: add check for group_list if the parent isn't counted | From | Peter Zijlstra <> | Date | Wed, 30 Dec 2009 13:28:45 +0100 |
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On Wed, 2009-12-30 at 19:28 +0800, Liming Wang wrote: > If the parent has no entry in group_list, child_ctx will not be > allocated, which will lead dereference of a NULL child_ctx.
That changelog sucks.
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?
In that case, would it not be better to change the if (inherited_all) condition to if (inherited_all && child_ctx) ?
> Signed-off-by: Liming Wang <liming.wang@windriver.com> > --- > kernel/perf_event.c | 2 ++ > 1 files changed, 2 insertions(+), 0 deletions(-) > > diff --git a/kernel/perf_event.c b/kernel/perf_event.c > index 5b987b4..3664c4b 100644 > --- a/kernel/perf_event.c > +++ b/kernel/perf_event.c > @@ -5126,6 +5126,8 @@ int perf_event_init_task(struct task_struct *child) > */ > mutex_lock(&parent_ctx->mutex); > > + if (list_empty(&parent_ctx->group_list)) > + goto exit; > /* > * We dont have to disable NMIs - we are only looking at > * the list, not manipulating it:
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