linux-kernel - Re: [PATCH] mutex: Report recursive ww

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Message-ID: <20160530091116.GP3192@twins.programming.kicks-ass.net>
Date:	Mon, 30 May 2016 11:11:16 +0200
From:	Peter Zijlstra <peterz@...radead.org>
To:	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
Cc:	Chris Wilson <chris@...is-wilson.co.uk>,
	Ingo Molnar <mingo@...hat.com>,
	intel-gfx@...ts.freedesktop.org,
	Christian König <christian.koenig@....com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] mutex: Report recursive ww_mutex locking early

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@...ux.intel.com>
> > Signed-off-by: Chris Wilson <chris@...is-wilson.co.uk>
> > Cc: Peter Zijlstra <peterz@...radead.org>
> > Cc: Ingo Molnar <mingo@...hat.com>
> > Cc: Christian König <christian.koenig@....com>
> > Cc: Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>
> > Cc: linux-kernel@...r.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@...ux.intel.com>
> 
> Should this be Cc: stable@...r.kernel.org ?

Can do; how far back?