Commit 0422e83d authored May 26, 2016 by Chris Wilson Committed by Ingo Molnar Jun 03, 2016

locking/ww_mutex: Report recursive ww_mutex locking early



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.

Suggested-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Link: http://lkml.kernel.org/r/1464293297-19777-1-git-send-email-chris@chris-wilson.co.uk


Signed-off-by: Ingo Molnar <mingo@kernel.org>

parent 55eed755

kernel/locking/mutex.c

+6 −3

Original line number	Original line	Diff line number	Diff line
	@@ -486,9 +486,6 @@ __ww_mutex_lock_check_stamp(struct mutex lock, struct ww_acquire_ctx ctx)
	if (!hold_ctx)		if (!hold_ctx)
	return 0;		return 0;

	if (unlikely(ctx == hold_ctx))
	return -EALREADY;

	if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&		if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
	(ctx->stamp != hold_ctx->stamp \|\| ctx > hold_ctx)) {		(ctx->stamp != hold_ctx->stamp \|\| ctx > hold_ctx)) {
	#ifdef CONFIG_DEBUG_MUTEXES		#ifdef CONFIG_DEBUG_MUTEXES
	@@ -514,6 +511,12 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
	unsigned long flags;		unsigned long flags;
	int ret;		int ret;

			if (use_ww_ctx) {
			struct ww_mutex *ww = container_of(lock, struct ww_mutex, base);
			if (unlikely(ww_ctx == READ_ONCE(ww->ctx)))
			return -EALREADY;
			}

	preempt_disable();		preempt_disable();
	mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);		mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);

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