+++ /dev/null
-From 0422e83d84ae24b933e4b0d4c1e0f0b4ae8a0a3b Mon Sep 17 00:00:00 2001
-From: Chris Wilson <chris@chris-wilson.co.uk>
-Date: Thu, 26 May 2016 21:08:17 +0100
-Subject: locking/ww_mutex: Report recursive ww_mutex locking early
-
-From: Chris Wilson <chris@chris-wilson.co.uk>
-
-commit 0422e83d84ae24b933e4b0d4c1e0f0b4ae8a0a3b upstream.
-
-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>
-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>
-Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-
----
- kernel/locking/mutex.c | 9 ++++++---
- 1 file changed, 6 insertions(+), 3 deletions(-)
-
---- a/kernel/locking/mutex.c
-+++ b/kernel/locking/mutex.c
-@@ -304,9 +304,6 @@ __mutex_lock_check_stamp(struct mutex *l
- if (!hold_ctx)
- return 0;
-
-- if (unlikely(ctx == hold_ctx))
-- return -EALREADY;
--
- if (ctx->stamp - hold_ctx->stamp <= LONG_MAX &&
- (ctx->stamp != hold_ctx->stamp || ctx > hold_ctx)) {
- #ifdef CONFIG_DEBUG_MUTEXES
-@@ -417,6 +414,12 @@ __mutex_lock_common(struct mutex *lock,
- unsigned long flags;
- 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();
- mutex_acquire_nest(&lock->dep_map, subclass, 0, nest_lock, ip);
-