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author | Nicolai Hähnle <Nicolai.Haehnle@amd.com> | 2016-12-21 19:46:35 +0100 |
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committer | Ingo Molnar <mingo@kernel.org> | 2017-01-14 11:14:43 +0100 |
commit | 200b1874401555e9b36010aa318e75cf57005f36 (patch) | |
tree | 646203e67ab11ee6b22d52c439ae0e969f4b4a5f /kernel | |
parent | locking/ww_mutex: Add waiters in stamp order (diff) | |
download | linux-200b1874401555e9b36010aa318e75cf57005f36.tar.xz linux-200b1874401555e9b36010aa318e75cf57005f36.zip |
locking/ww_mutex: Notify waiters that have to back off while adding tasks to wait list
While adding our task as a waiter, detect if another task should back off
because of us.
With this patch, we establish the invariant that the wait list contains
at most one (sleeping) waiter with ww_ctx->acquired > 0, and this waiter
will be the first waiter with a context.
Since only waiters with ww_ctx->acquired > 0 have to back off, this allows
us to be much more economical with wakeups.
Signed-off-by: Nicolai Hähnle <Nicolai.Haehnle@amd.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Maarten Lankhorst <dev@mblankhorst.nl>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: dri-devel@lists.freedesktop.org
Link: http://lkml.kernel.org/r/1482346000-9927-8-git-send-email-nhaehnle@gmail.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel')
-rw-r--r-- | kernel/locking/mutex.c | 40 |
1 files changed, 30 insertions, 10 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c index d0f7628b5a3d..66967219477d 100644 --- a/kernel/locking/mutex.c +++ b/kernel/locking/mutex.c @@ -596,23 +596,34 @@ void __sched ww_mutex_unlock(struct ww_mutex *lock) EXPORT_SYMBOL(ww_mutex_unlock); static inline int __sched -__ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx) +__ww_mutex_lock_check_stamp(struct mutex *lock, struct mutex_waiter *waiter, + struct ww_acquire_ctx *ctx) { struct ww_mutex *ww = container_of(lock, struct ww_mutex, base); struct ww_acquire_ctx *hold_ctx = READ_ONCE(ww->ctx); + struct mutex_waiter *cur; - if (!hold_ctx) - return 0; + if (hold_ctx && __ww_ctx_stamp_after(ctx, hold_ctx)) + goto deadlock; - if (__ww_ctx_stamp_after(ctx, hold_ctx)) { -#ifdef CONFIG_DEBUG_MUTEXES - DEBUG_LOCKS_WARN_ON(ctx->contending_lock); - ctx->contending_lock = ww; -#endif - return -EDEADLK; + /* + * If there is a waiter in front of us that has a context, then its + * stamp is earlier than ours and we must back off. + */ + cur = waiter; + list_for_each_entry_continue_reverse(cur, &lock->wait_list, list) { + if (cur->ww_ctx) + goto deadlock; } return 0; + +deadlock: +#ifdef CONFIG_DEBUG_MUTEXES + DEBUG_LOCKS_WARN_ON(ctx->contending_lock); + ctx->contending_lock = ww; +#endif + return -EDEADLK; } static inline int __sched @@ -655,6 +666,15 @@ __ww_mutex_add_waiter(struct mutex_waiter *waiter, } pos = &cur->list; + + /* + * Wake up the waiter so that it gets a chance to back + * off. + */ + if (cur->ww_ctx->acquired > 0) { + debug_mutex_wake_waiter(lock, cur); + wake_up_process(cur->task); + } } list_add_tail(&waiter->list, pos); @@ -746,7 +766,7 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass, } if (use_ww_ctx && ww_ctx && ww_ctx->acquired > 0) { - ret = __ww_mutex_lock_check_stamp(lock, ww_ctx); + ret = __ww_mutex_lock_check_stamp(lock, &waiter, ww_ctx); if (ret) goto err; } |