On Sun, Jan 25, 2015 at 04:34:28AM +0000, Fengguang Wu wrote: > Greetings,
Hi Fengguang, Thanks very much for the report. > 0day kernel testing robot got the below dmesg and the first bad commit is > > git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git perf/core > > commit d26bb7f73a2881f2412c340a27438b185f0cc3dc > Author: Mark Rutland <mark.rutl...@arm.com> > AuthorDate: Wed Jan 7 15:01:54 2015 +0000 > Commit: Peter Zijlstra <pet...@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 in perf_event_task_tick. 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 explosions. Peter, I guess you'll drop this patch for now? Thanks, Mark. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
