seqlock: fix seqlock_write_unlock_impl function

The seqlock write unlock function was incorrectly calling
seqlock_write_begin() instead of seqlock_write_end(), and was releasing
the lock before incrementing the sequence. This could lead to a race
condition and a corrupted sequence number becoming odd even though the
lock is not held.

Signed-off-by: Luc Michel <luc.michel@greensocs.com>
Reviewed-by: Philippe Mathieu-Daudé <philmd@redhat.com>
Message-Id: <20200129144948.2161551-1-luc.michel@greensocs.com>
Fixes: 988fcafc73 ("seqlock: add QemuLockable support", 2018-08-23)
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>

diff --git a/include/qemu/seqlock.h b/include/qemu/seqlock.h
index fd408b7ec543029249e518c0666879d167eaab82..8b6b4ee4bbcf6a80fee192125afdff21a358a7c5 100644 (file)
--- a/include/qemu/seqlock.h
+++ b/include/qemu/seqlock.h
@@ -55,11 +55,11 @@ static inline void seqlock_write_lock_impl(QemuSeqLock *sl, QemuLockable *lock)
 #define seqlock_write_lock(sl, lock) \
     seqlock_write_lock_impl(sl, QEMU_MAKE_LOCKABLE(lock))
 
-/* Lock out other writers and update the count.  */
+/* Update the count and release the lock.  */
 static inline void seqlock_write_unlock_impl(QemuSeqLock *sl, QemuLockable *lock)
 {
+    seqlock_write_end(sl);
     qemu_lockable_unlock(lock);
-    seqlock_write_begin(sl);
 }
 #define seqlock_write_unlock(sl, lock) \
     seqlock_write_unlock_impl(sl, QEMU_MAKE_LOCKABLE(lock))