On Wed, Jan 07, 2015 at 03:01:54PM +0000, Mark Rutland wrote:
> Currently the adjusments made as part of perf_event_task_tick use the
> percpu rotation lists to iterate over any active PMU contexts, but these
> are not used by the context rotation code, having been replaced by
> separate (per-context) hrtimer callbacks. However, some manipulation of
> the rotation lists (i.e. removal of contexts) has remained in
> perf_rotate_context. This leads to the following issues:
>
> * Contexts are not always removed from the rotation lists. Removal of
> PMUs which have been placed in rotation lists, but have not been
> removed by a hrtimer callback can result in corruption of the rotation
> lists (when memory backing the context is freed).
>
> This has been observed to result in hangs when PMU drivers built as
> modules are inserted and removed around the creation of events for
> said PMUs.
>
> * Contexts which do not require rotation may be removed from the
> rotation lists as a result of a hrtimer, and will not be considered by
> the unthrottling code in perf_event_task_tick.
>
> This patch solves these issues by moving any and all removal of contexts
> from rotation lists to only occur when the final event is removed from a
> context, mirroring the addition which only occurs when the first event
> is added to a context. The vestigal manipulation of the rotation lists
> is removed from perf_event_rotate_context.
>
> As the rotation_list variables are not used for rotation, these are
> renamed to active_ctx_list, which better matches their current function.
> perf_pmu_rotate_{start,stop} are renamed to
> perf_pmu_ctx_{activate,deactivate}.
>
> Signed-off-by: Mark Rutland <[email protected]>
> Reported-by: Johannes Jensen <[email protected]>
> Cc: Will Deacon <[email protected]>
> Cc: Peter Zijlstra <[email protected]>
> Cc: Paul Mackerras <[email protected]>
> Cc: Ingo Molnar <[email protected]>
> Cc: Arnaldo Carvalho de Melo <[email protected]>
Thanks!
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
