Re: [PATCH] mutex: Report recursive ww_mutex locking early

Peter Zijlstra
2016-05-30T09:11:24Z

On Mon, May 30, 2016 at 09:43:53AM +0200, Maarten Lankhorst wrote:
> Op 26-05-16 om 22:08 schreef Chris Wilson:
> > Recursive locking for ww_mutexes was originally conceived as an
> > exception. However, it is heavily used by the DRM atomic modesetting
> > code. Currently, the recursive deadlock is checked after we have queued
> > up for a busy-spin and as we never release the lock, we spin until
> > kicked, whereupon the deadlock is discovered and reported.
> >
> > A simple solution for the now common problem is to move the recursive
> > deadlock discovery to the first action when taking the ww_mutex.
> >
> > Testcase: igt/kms_cursor_legacy

I've no idea what this tag is or where to find the actual testcase, so
I've killed it.

> > Suggested-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
> > Cc: Peter Zijlstra <peterz@infradead.org>
> > Cc: Ingo Molnar <mingo@redhat.com>
> > Cc: Christian König <christian.koenig@amd.com>
> > Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
> > Cc: linux-kernel@vger.kernel.org
> > ---
> >
> > Maarten suggested this as a simpler fix to the immediate problem. Imo,
> > we still want to perform deadlock detection within the spin in order to
> > catch more complicated deadlocks without osq_lock() forcing fairness!
> Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>
> Should this be Cc: stable@vger.kernel.org ?

Can do; how far back?