diff options
Diffstat (limited to 'common/recipes-kernel/linux/files/1141-Fix-a-deadlock-affecting-ww_mutexes.patch')
| -rw-r--r-- | common/recipes-kernel/linux/files/1141-Fix-a-deadlock-affecting-ww_mutexes.patch | 121 |
1 files changed, 0 insertions, 121 deletions
diff --git a/common/recipes-kernel/linux/files/1141-Fix-a-deadlock-affecting-ww_mutexes.patch b/common/recipes-kernel/linux/files/1141-Fix-a-deadlock-affecting-ww_mutexes.patch deleted file mode 100644 index 25312ef1..00000000 --- a/common/recipes-kernel/linux/files/1141-Fix-a-deadlock-affecting-ww_mutexes.patch +++ /dev/null @@ -1,121 +0,0 @@ -From 5f3c992c00f95a483cf01d55b8ff0fa1fe6df216 Mon Sep 17 00:00:00 2001 -From: Sanjay R Mehta <sanju.mehta@amd.com> -Date: Wed, 23 Nov 2016 14:54:46 +0530 -Subject: [PATCH 03/10] Fix a deadlock affecting ww_mutexes -MIME-Version: 1.0 -Content-Type: text/plain; charset=UTF-8 -Content-Transfer-Encoding: 8bit - -his patch fixes a race condition involving 4 threads and 2 ww_mutexes -as indicated in the following example. Acquire context stamps are ordered -like the thread numbers, i.e. thread #1 should back off when it encounters -a mutex locked by thread #0 etc. - -Thread #0 Thread #1 Thread #2 Thread #3 ---------- --------- --------- --------- - lock(ww) - lock(ww') - lock(ww) - lock(ww) - unlock(ww) part 1 -lock(ww) - unlock(ww) part 2 - back off -lock(ww') - -Here, unlock(ww) part 1 is the part that sets lock->base.count to 1 -(without being protected by lock->base.wait_lock), meaning that thread #0 -can acquire ww in the fast path. Since lock->base.count == 0, thread #0 -won't wake up any of the waiters. - -Then, unlock(ww) part 2 wakes up _only_the_first_ waiter of ww. This is -thread #2, since waiters are added at the tail. Thread #2 wakes up and -backs off since it sees ww owned by a context with a lower stamp. - -Meanwhile, thread #1 is never woken up, and so it won't back off its lock -on ww'. So thread #0 gets stuck waiting for ww' to be released. - -This patch fixes the deadlock by waking up all waiters in the slow path -of ww_mutex_unlock. - -We have an internal test case for amdgpu which continuously submits -command streams from tens of threads, where all command stream reference -hundreds of GPU buffer objects with a lot of overlap in the buffer lists -between command streams. This test reliably caused a deadlock, and while I -haven't completely confirmed that it is exactly the scenario outlined -above, this patch does fix the test case. - -Signed-off-by: Nicolai Hähnle <nicolai.haehnle@amd.com> -Signed-off-by: Sanjay R Mehta <sanju.mehta@amd.com> ---- - kernel/locking/mutex.c | 26 ++++++++++++++++++++++---- - 1 file changed, 22 insertions(+), 4 deletions(-) - -diff --git a/kernel/locking/mutex.c b/kernel/locking/mutex.c -index 0551c21..39fa58a 100644 ---- a/kernel/locking/mutex.c -+++ b/kernel/locking/mutex.c -@@ -409,6 +409,10 @@ static bool mutex_optimistic_spin(struct mutex *lock, - __visible __used noinline - void __sched __mutex_unlock_slowpath(atomic_t *lock_count); - -+static __used noinline -+void __sched __mutex_unlock_slowpath_wakeall(atomic_t *lock_count); -+ -+ - /** - * mutex_unlock - release the mutex - * @lock: the mutex to be released -@@ -473,7 +477,7 @@ void __sched ww_mutex_unlock(struct ww_mutex *lock) - */ - mutex_clear_owner(&lock->base); - #endif -- __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath); -+ __mutex_fastpath_unlock(&lock->base.count, __mutex_unlock_slowpath_wakeall); - } - EXPORT_SYMBOL(ww_mutex_unlock); - -@@ -713,7 +717,7 @@ EXPORT_SYMBOL_GPL(__ww_mutex_lock_interruptible); - * Release the lock, slowpath: - */ - static inline void --__mutex_unlock_common_slowpath(struct mutex *lock, int nested) -+__mutex_unlock_common_slowpath(struct mutex *lock, int nested, int wake_all) - { - unsigned long flags; - -@@ -736,7 +740,13 @@ __mutex_unlock_common_slowpath(struct mutex *lock, int nested) - mutex_release(&lock->dep_map, nested, _RET_IP_); - debug_mutex_unlock(lock); - -- if (!list_empty(&lock->wait_list)) { -+ if (wake_all) { -+ struct mutex_waiter *waiter; -+ list_for_each_entry(waiter, &lock->wait_list, list) { -+ debug_mutex_wake_waiter(lock, waiter); -+ wake_up_process(waiter->task); -+ } -+ } else if (!list_empty(&lock->wait_list)) { - /* get the first entry from the wait-list: */ - struct mutex_waiter *waiter = - list_entry(lock->wait_list.next, -@@ -758,7 +768,15 @@ __mutex_unlock_slowpath(atomic_t *lock_count) - { - struct mutex *lock = container_of(lock_count, struct mutex, count); - -- __mutex_unlock_common_slowpath(lock, 1); -+ __mutex_unlock_common_slowpath(lock, 1, 0); -+} -+ -+static void -+__mutex_unlock_slowpath_wakeall(atomic_t *lock_count) -+{ -+ struct mutex *lock = container_of(lock_count, struct mutex, count); -+ -+ __mutex_unlock_common_slowpath(lock, 1, 1); - } - - #ifndef CONFIG_DEBUG_LOCK_ALLOC --- -2.7.4 - |