On Tue, Sep 02, 2014 at 03:27:20PM -0700, Cong Wang wrote: > From: Cong Wang <cw...@twopensource.com> > > We saw a kernel soft lockup in perf_remove_from_context(), > it looks like the `perf` process, when exiting, could not go > out of the retry loop. Meanwhile, the target process was forking > a child. So either the target process should execute the smp > function call to deactive the event (if it was running) or it should > do a context switch which deactives the event. > > It seems we optimize out a context switch in perf_event_context_sched_out(), > and what's more important, we still test an obsolete task pointer when > retrying, so no one actually would deactive that event in this situation. > Fix it directly by reloading the task pointer in perf_remove_from_context(). > This should cure the above soft lockup. > > Cc: stable@vger.kernel.org > Cc: Peter Zijlstra <a.p.zijls...@chello.nl> > Cc: Paul Mackerras <pau...@samba.org> > Cc: Ingo Molnar <mi...@redhat.com> > Cc: Arnaldo Carvalho de Melo <a...@kernel.org> > Signed-off-by: Cong Wang <cw...@twopensource.com> > Signed-off-by: Cong Wang <xiyou.wangc...@gmail.com>
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