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authorLinus Torvalds <torvalds@linux-foundation.org>2016-06-10 19:53:46 +0200
committerLinus Torvalds <torvalds@linux-foundation.org>2016-06-10 19:53:46 +0200
commit02b07bde619e179bf7ac0e073d28e2e038dfab77 (patch)
tree47f3ce1a56cb4c7dd46f208d6c13208ef7ec900f /include
parentMerge branch 'efi-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/ker... (diff)
parentfutex: Calculate the futex key based on a tail page for file-based futexes (diff)
downloadlinux-02b07bde619e179bf7ac0e073d28e2e038dfab77.tar.xz
linux-02b07bde619e179bf7ac0e073d28e2e038dfab77.zip
Merge branch 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip
Pull locking fixes from Ingo Molnar: "Misc fixes: - a file-based futex fix - one more spin_unlock_wait() fix - a ww-mutex deadlock detection improvement/fix - and a raw_read_seqcount_latch() barrier fix" * 'locking-urgent-for-linus' of git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip: futex: Calculate the futex key based on a tail page for file-based futexes locking/qspinlock: Fix spin_unlock_wait() some more locking/ww_mutex: Report recursive ww_mutex locking early locking/seqcount: Re-fix raw_read_seqcount_latch()
Diffstat (limited to 'include')
-rw-r--r--include/asm-generic/qspinlock.h53
-rw-r--r--include/linux/seqlock.h7
2 files changed, 22 insertions, 38 deletions
diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h
index 6bd05700d8c9..05f05f17a7c2 100644
--- a/include/asm-generic/qspinlock.h
+++ b/include/asm-generic/qspinlock.h
@@ -22,37 +22,33 @@
#include <asm-generic/qspinlock_types.h>
/**
+ * queued_spin_unlock_wait - wait until the _current_ lock holder releases the lock
+ * @lock : Pointer to queued spinlock structure
+ *
+ * There is a very slight possibility of live-lock if the lockers keep coming
+ * and the waiter is just unfortunate enough to not see any unlock state.
+ */
+#ifndef queued_spin_unlock_wait
+extern void queued_spin_unlock_wait(struct qspinlock *lock);
+#endif
+
+/**
* queued_spin_is_locked - is the spinlock locked?
* @lock: Pointer to queued spinlock structure
* Return: 1 if it is locked, 0 otherwise
*/
+#ifndef queued_spin_is_locked
static __always_inline int queued_spin_is_locked(struct qspinlock *lock)
{
/*
- * queued_spin_lock_slowpath() can ACQUIRE the lock before
- * issuing the unordered store that sets _Q_LOCKED_VAL.
- *
- * See both smp_cond_acquire() sites for more detail.
- *
- * This however means that in code like:
- *
- * spin_lock(A) spin_lock(B)
- * spin_unlock_wait(B) spin_is_locked(A)
- * do_something() do_something()
- *
- * Both CPUs can end up running do_something() because the store
- * setting _Q_LOCKED_VAL will pass through the loads in
- * spin_unlock_wait() and/or spin_is_locked().
+ * See queued_spin_unlock_wait().
*
- * Avoid this by issuing a full memory barrier between the spin_lock()
- * and the loads in spin_unlock_wait() and spin_is_locked().
- *
- * Note that regular mutual exclusion doesn't care about this
- * delayed store.
+ * Any !0 state indicates it is locked, even if _Q_LOCKED_VAL
+ * isn't immediately observable.
*/
- smp_mb();
- return atomic_read(&lock->val) & _Q_LOCKED_MASK;
+ return atomic_read(&lock->val);
}
+#endif
/**
* queued_spin_value_unlocked - is the spinlock structure unlocked?
@@ -122,21 +118,6 @@ static __always_inline void queued_spin_unlock(struct qspinlock *lock)
}
#endif
-/**
- * queued_spin_unlock_wait - wait until current lock holder releases the lock
- * @lock : Pointer to queued spinlock structure
- *
- * There is a very slight possibility of live-lock if the lockers keep coming
- * and the waiter is just unfortunate enough to not see any unlock state.
- */
-static inline void queued_spin_unlock_wait(struct qspinlock *lock)
-{
- /* See queued_spin_is_locked() */
- smp_mb();
- while (atomic_read(&lock->val) & _Q_LOCKED_MASK)
- cpu_relax();
-}
-
#ifndef virt_spin_lock
static __always_inline bool virt_spin_lock(struct qspinlock *lock)
{
diff --git a/include/linux/seqlock.h b/include/linux/seqlock.h
index 7973a821ac58..ead97654c4e9 100644
--- a/include/linux/seqlock.h
+++ b/include/linux/seqlock.h
@@ -277,7 +277,10 @@ static inline void raw_write_seqcount_barrier(seqcount_t *s)
static inline int raw_read_seqcount_latch(seqcount_t *s)
{
- return lockless_dereference(s)->sequence;
+ int seq = READ_ONCE(s->sequence);
+ /* Pairs with the first smp_wmb() in raw_write_seqcount_latch() */
+ smp_read_barrier_depends();
+ return seq;
}
/**
@@ -331,7 +334,7 @@ static inline int raw_read_seqcount_latch(seqcount_t *s)
* unsigned seq, idx;
*
* do {
- * seq = lockless_dereference(latch)->seq;
+ * seq = raw_read_seqcount_latch(&latch->seq);
*
* idx = seq & 0x01;
* entry = data_query(latch->data[idx], ...);