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authorNicolai Hähnle <Nicolai.Haehnle@amd.com>2016-12-21 19:46:34 +0100
committerIngo Molnar <mingo@kernel.org>2017-01-14 11:14:42 +0100
commit6baa5c60a97d7f1a37a4b5ab5fb3a450e56e8b06 (patch)
tree738389ea7ecce34a3c8db1046fe2a8e1c24d64d1 /kernel/locking/mutex.c
parentc5470b22d1833241cae996d23a8a346ff8ec4d58 (diff)
downloadlinux-6baa5c60a97d7f1a37a4b5ab5fb3a450e56e8b06.tar.bz2
locking/ww_mutex: Add waiters in stamp order
Add regular waiters in stamp order. Keep adding waiters that have no context in FIFO order and take care not to starve them. While adding our task as a waiter, back off if we detect that there is a waiter with a lower stamp in front of us. Make sure to call lock_contended even when we back off early. For w/w mutexes, being first in the wait list is only stable when taking the lock without a context. Therefore, the purpose of the first flag is split into two: 'first' remains to indicate whether we want to spin optimistically, while 'handoff' indicates that we should be prepared to accept a handoff. For w/w locking with a context, we always accept handoffs after the first schedule(), to handle the following sequence of events: 1. Task #0 unlocks and hands off to Task #2 which is first in line 2. Task #1 adds itself in front of Task #2 3. Task #2 wakes up and must accept the handoff even though it is no longer first in line Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Cc: =?UTF-8?q?Nicolai=20H=C3=A4hnle?= <Nicolai.Haehnle@amd.com> 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/1482346000-9927-7-git-send-email-nhaehnle@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
Diffstat (limited to 'kernel/locking/mutex.c')
-rw-r--r--kernel/locking/mutex.c76
1 files changed, 69 insertions, 7 deletions
diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c
index c696614a6b8b..d0f7628b5a3d 100644
--- a/kernel/locking/mutex.c
+++ b/kernel/locking/mutex.c
@@ -615,6 +615,52 @@ __ww_mutex_lock_check_stamp(struct mutex *lock, struct ww_acquire_ctx *ctx)
return 0;
}
+static inline int __sched
+__ww_mutex_add_waiter(struct mutex_waiter *waiter,
+ struct mutex *lock,
+ struct ww_acquire_ctx *ww_ctx)
+{
+ struct mutex_waiter *cur;
+ struct list_head *pos;
+
+ if (!ww_ctx) {
+ list_add_tail(&waiter->list, &lock->wait_list);
+ return 0;
+ }
+
+ /*
+ * Add the waiter before the first waiter with a higher stamp.
+ * Waiters without a context are skipped to avoid starving
+ * them.
+ */
+ pos = &lock->wait_list;
+ list_for_each_entry_reverse(cur, &lock->wait_list, list) {
+ if (!cur->ww_ctx)
+ continue;
+
+ if (__ww_ctx_stamp_after(ww_ctx, cur->ww_ctx)) {
+ /* Back off immediately if necessary. */
+ if (ww_ctx->acquired > 0) {
+#ifdef CONFIG_DEBUG_MUTEXES
+ struct ww_mutex *ww;
+
+ ww = container_of(lock, struct ww_mutex, base);
+ DEBUG_LOCKS_WARN_ON(ww_ctx->contending_lock);
+ ww_ctx->contending_lock = ww;
+#endif
+ return -EDEADLK;
+ }
+
+ break;
+ }
+
+ pos = &cur->list;
+ }
+
+ list_add_tail(&waiter->list, pos);
+ return 0;
+}
+
/*
* Lock a mutex (possibly interruptible), slowpath:
*/
@@ -659,15 +705,25 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
debug_mutex_lock_common(lock, &waiter);
debug_mutex_add_waiter(lock, &waiter, current);
- /* add waiting tasks to the end of the waitqueue (FIFO): */
- list_add_tail(&waiter.list, &lock->wait_list);
+ lock_contended(&lock->dep_map, ip);
+
+ if (!use_ww_ctx) {
+ /* add waiting tasks to the end of the waitqueue (FIFO): */
+ list_add_tail(&waiter.list, &lock->wait_list);
+ } else {
+ /* Add in stamp order, waking up waiters that must back off. */
+ ret = __ww_mutex_add_waiter(&waiter, lock, ww_ctx);
+ if (ret)
+ goto err_early_backoff;
+
+ waiter.ww_ctx = ww_ctx;
+ }
+
waiter.task = current;
if (__mutex_waiter_is_first(lock, &waiter))
__mutex_set_flag(lock, MUTEX_FLAG_WAITERS);
- lock_contended(&lock->dep_map, ip);
-
set_current_state(state);
for (;;) {
/*
@@ -698,9 +754,14 @@ __mutex_lock_common(struct mutex *lock, long state, unsigned int subclass,
spin_unlock_mutex(&lock->wait_lock, flags);
schedule_preempt_disabled();
- if (!first && __mutex_waiter_is_first(lock, &waiter)) {
- first = true;
- __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
+ /*
+ * ww_mutex needs to always recheck its position since its waiter
+ * list is not FIFO ordered.
+ */
+ if ((use_ww_ctx && ww_ctx) || !first) {
+ first = __mutex_waiter_is_first(lock, &waiter);
+ if (first)
+ __mutex_set_flag(lock, MUTEX_FLAG_HANDOFF);
}
set_current_state(state);
@@ -739,6 +800,7 @@ skip_wait:
err:
__set_current_state(TASK_RUNNING);
mutex_remove_waiter(lock, &waiter, current);
+err_early_backoff:
spin_unlock_mutex(&lock->wait_lock, flags);
debug_mutex_free_waiter(&waiter);
mutex_release(&lock->dep_map, 1, ip);