On Sun, Jan 25, 2015 at 04:34:28AM +0000, Fengguang Wu wrote:
Thanks very much for the report.
0day kernel testing robot got the below dmesg and the first bad
Author: Mark Rutland <mark.rutland(a)arm.com>
AuthorDate: Wed Jan 7 15:01:54 2015 +0000
Commit: Peter Zijlstra <peterz(a)infradead.org>
CommitDate: Fri Jan 23 15:17:56 2015 +0100
perf: decouple unthrottling and rotating
What seems to be happening is:
* An event is created in the context of task A on CPU0. As the task's hw
context is empty of events, we call perf_pmu_ctx_activate. This adds
the cpuctx of the relevant HW PMU to the active_ctx_list. Note that we
checked the task's ctx for emptiness, then added the PMU's hw context.
* An event is created (as a result of a clone()) in the context of task
B on CPU0, and we do the same thing, finding the ctx empty of events
we add the HW PMU's cpuctx to the active_ctx_list. As it's already in
there, the WARN_ON(!list_empty(&cpuctx->active_ctx_list)) explodes.
So I guess what we actually want to do is to turn the active_ctx list
into a list of perf_event_contexts rather than perf_event_cpu_contexts,
and add/remove from the list when a context is scheduled in/out (or
updated empty<->nonempty). That way we remove chances for erroneous
add/remove, and we don't need to treat task and CPU contexts separately
I managed to get the reproducer running on a box at home, so I'll spin a
potential fix against that for a while, and send that out if I don't see
Peter, I guess you'll drop this patch for now?