Commit 0f5225b0 authored by Peter Zijlstra's avatar Peter Zijlstra Committed by Ingo Molnar
Browse files

locking/mutex, drm: Introduce mutex_trylock_recursive() 



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.

Signed-off-by: default avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: David Airlie <airlied@linux.ie>
Cc: Davidlohr Bueso <dave@stgolabs.net>
Cc: Ding Tianhong <dingtianhong@huawei.com>
Cc: Imre Deak <imre.deak@intel.com>
Cc: Jason Low <jason.low2@hpe.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@us.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Rob Clark <robdclark@gmail.com>
Cc: Terry Rudd <terry.rudd@hpe.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Tim Chen <tim.c.chen@linux.intel.com>
Cc: Will Deacon <Will.Deacon@arm.com>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: default avatarIngo Molnar <mingo@kernel.org>
parent 83f06168

drivers/gpu/drm/i915/i915_gem_shrinker.c

+12 −3
Original line number Diff line number Diff line
@@ -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;



	case MUTEX_TRYLOCK_SUCCESS:

		*unlock = true;

		return true;



	case MUTEX_TRYLOCK_RECURSIVE:

		*unlock = false;

		return true;

	}



	BUG();

}



static unsigned long

drivers/gpu/drm/msm/msm_gem_shrinker.c

+12 −4
Original line number Diff line number Diff line
@@ -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;



	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)

include/linux/mutex.h

+31 −0
Original line number Diff line number Diff line
@@ -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 */

scripts/checkpatch.pl

+6 −0
Original line number Diff line number Diff line
@@ -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*\)/ ) {

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