On Tue, 27 May 2014, Vince Weaver wrote:
> On Tue, 27 May 2014, Vince Weaver wrote:
>
> > OK, the problem is in:
> >
> > kernel/events/core.c find_get_context()
> >
> > retry:
> > perf_lock_task_context() returns NULL.
> > alloc_perf_context()
> > task->perf_event_ctxp[ctxn] is *not* NULL
> > err == EAGAIN so jump to retry
> >
so after sticking some trace_printk()s in the code, it turns out
that for the software PMU
perf_lock_task_context() returns NULL beause
!atomic_inc_not_zero(&ctx->refcount)
is zero, but
task->perf_event_ctxp[ctxn] still has a value.
And since those conditions never change it just loops forever, stuck.
I'm not sure how the reference count is getting messed up.
This is reproducible so if there's anything useful I can turn on
tracing-wise let me know.
Vince
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