From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753047AbcKIKif (ORCPT ); Wed, 9 Nov 2016 05:38:35 -0500 Received: from bombadil.infradead.org ([198.137.202.9]:43354 "EHLO bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1750877AbcKIKid (ORCPT ); Wed, 9 Nov 2016 05:38:33 -0500 Date: Wed, 9 Nov 2016 11:38:13 +0100 From: Peter Zijlstra To: Linus Torvalds , Waiman Long , Jason Low , Ding Tianhong , Thomas Gleixner , Will Deacon , Ingo Molnar , Imre Deak , Linux Kernel Mailing List , Davidlohr Bueso , Tim Chen , Terry Rudd , "Paul E. McKenney" Cc: Chris Wilson , Daniel Vetter , Rob Clark Subject: Re: [PATCH -v4 1/8] locking/drm: Kill mutex trickery Message-ID: <20161109103813.GN3157@twins.programming.kicks-ass.net> References: <20161007145243.361481786@infradead.org> <20161007150210.927453282@infradead.org> <20161007154351.GL3117@twins.programming.kicks-ass.net> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20161007154351.GL3117@twins.programming.kicks-ass.net> User-Agent: Mutt/1.5.23.1 (2014-03-12) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Fri, Oct 07, 2016 at 05:43:51PM +0200, Peter Zijlstra wrote: > On Fri, Oct 07, 2016 at 04:52:44PM +0200, Peter Zijlstra wrote: > > Poking at lock internals is not cool. Since I'm going to change the > > implementation this will break, take it out. > > > So something like the below would serve as a replacement for your > previous hacks. Is this API something acceptable to people? Compile tested only.. Daniel reminded me in another thread. --- Subject: locking/mutex,drm: Introduce mutex_trylock_recursive() From: Peter Zijlstra Date: Fri, 7 Oct 2016 17:43:51 +0200 By popular DRM demand, introduce mutex_trylock_recursive() to fix up the two GEM users. Without this it is very easy for these drivers to get stuck in low-memory situations and trigger OOM. Work is in progress to remove the need for this in at least i915. Cc: Daniel Vetter Cc: Chris Wilson Cc: Rob Clark Signed-off-by: Peter Zijlstra (Intel) --- drivers/gpu/drm/i915/i915_gem_shrinker.c | 15 ++++++++++++--- drivers/gpu/drm/msm/msm_gem_shrinker.c | 16 ++++++++++++---- include/linux/mutex.h | 31 +++++++++++++++++++++++++++++++ scripts/checkpatch.pl | 6 ++++++ 4 files changed, 61 insertions(+), 7 deletions(-) diff --git a/drivers/gpu/drm/i915/i915_gem_shrinker.c b/drivers/gpu/drm/i915/i915_gem_shrinker.c index e9bd2a81d03a..5543d993a50e 100644 --- a/drivers/gpu/drm/i915/i915_gem_shrinker.c +++ b/drivers/gpu/drm/i915/i915_gem_shrinker.c @@ -227,11 +227,20 @@ unsigned long i915_gem_shrink_all(struct drm_i915_private *dev_priv) static bool i915_gem_shrinker_lock(struct drm_device *dev, bool *unlock) { - if (!mutex_trylock(&dev->struct_mutex)) + switch (mutex_trylock_recursive(&dev->struct_mutex)) { + case MUTEX_TRYLOCK_FAILED: return false; - *unlock = true; - return true; + case MUTEX_TRYLOCK_SUCCESS: + *unlock = true; + return true; + + case MUTEX_TRYLOCK_RECURSIVE: + *unlock = false; + return true; + } + + BUG(); } static unsigned long diff --git a/drivers/gpu/drm/msm/msm_gem_shrinker.c b/drivers/gpu/drm/msm/msm_gem_shrinker.c index 6d2e885bd58e..62b8cc653823 100644 --- a/drivers/gpu/drm/msm/msm_gem_shrinker.c +++ b/drivers/gpu/drm/msm/msm_gem_shrinker.c @@ -20,13 +20,21 @@ static bool msm_gem_shrinker_lock(struct drm_device *dev, bool *unlock) { - if (!mutex_trylock(&dev->struct_mutex)) + switch (mutex_trylock_recursive(&dev->struct_mutex)) { + case MUTEX_TRYLOCK_FAILED: return false; - *unlock = true; - return true; -} + case MUTEX_TRYLOCK_SUCCESS: + *unlock = true; + return true; + case MUTEX_TRYLOCK_RECURSIVE: + *unlock = false; + return true; + } + + BUG(); +} static unsigned long msm_gem_shrinker_count(struct shrinker *shrinker, struct shrink_control *sc) diff --git a/include/linux/mutex.h b/include/linux/mutex.h index 4d3bccabbea5..6a902f0a2148 100644 --- a/include/linux/mutex.h +++ b/include/linux/mutex.h @@ -189,4 +189,35 @@ extern void mutex_unlock(struct mutex *lock); extern int atomic_dec_and_mutex_lock(atomic_t *cnt, struct mutex *lock); +/* + * These values are chosen such that FAIL and SUCCESS match the + * values of the regular mutex_trylock(). + */ +enum mutex_trylock_recursive_enum { + MUTEX_TRYLOCK_FAILED = 0, + MUTEX_TRYLOCK_SUCCESS = 1, + MUTEX_TRYLOCK_RECURSIVE, +}; + +/** + * mutex_trylock_recursive - trylock variant that allows recursive locking + * @lock: mutex to be locked + * + * This function should not be used, _ever_. It is purely for hysterical GEM + * raisins, and once those are gone this will be removed. + * + * Returns: + * MUTEX_TRYLOCK_FAILED - trylock failed, + * MUTEX_TRYLOCK_SUCCESS - lock acquired, + * MUTEX_TRYLOCK_RECURSIVE - we already owned the lock. + */ +static inline __deprecated __must_check enum mutex_trylock_recursive_enum +mutex_trylock_recursive(struct mutex *lock) +{ + if (unlikely(__mutex_owner(lock) == current)) + return MUTEX_TRYLOCK_RECURSIVE; + + return mutex_trylock(lock); +} + #endif /* __LINUX_MUTEX_H */ diff --git a/scripts/checkpatch.pl b/scripts/checkpatch.pl index a8368d1c4348..23f462f64a3f 100755 --- a/scripts/checkpatch.pl +++ b/scripts/checkpatch.pl @@ -6076,6 +6076,12 @@ sub process { } } +# check for mutex_trylock_recursive usage + if ($line =~ /mutex_trylock_recursive/) { + ERROR("LOCKING", + "recursive locking is bad, do not use this ever.\n" . $herecurr); + } + # check for lockdep_set_novalidate_class if ($line =~ /^.\s*lockdep_set_novalidate_class\s*\(/ || $line =~ /__lockdep_no_validate__\s*\)/ ) {