Commit-ID: 0422e83d84ae24b933e4b0d4c1e0f0b4ae8a0a3b Gitweb: http://git.kernel.org/tip/0422e83d84ae24b933e4b0d4c1e0f0b4ae8a0a3b Author: Chris Wilson <[email protected]> AuthorDate: Thu, 26 May 2016 21:08:17 +0100 Committer: Ingo Molnar <[email protected]> CommitDate: Fri, 3 Jun 2016 08:37:26 +0200
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 <[email protected]> Signed-off-by: Chris Wilson <[email protected]> Signed-off-by: Peter Zijlstra (Intel) <[email protected]> Reviewed-by: Maarten Lankhorst <[email protected]> Cc: Andrew Morton <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Paul E. McKenney <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: [email protected] Link: http://lkml.kernel.org/r/[email protected] Signed-off-by: Ingo Molnar <[email protected]> --- kernel/locking/mutex.c | 9 ++++++--- 1 file changed, 6 insertions(+), 3 deletions(-) diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index e364b42..79d2d76 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -486,9 +486,6 @@ __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx) 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, long state, unsigned int subclass, 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);
