| 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 |
| @@ -486,9 +486,6 @@ __ww_mutex_lock_check_stamp(struct mutex |
| 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 |
| @@ -514,6 +511,12 @@ __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); |
| |