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seqlock: fix seqlock_write_unlock_impl function

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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>
This commit is contained in:
Chen Qun 2020-01-29 15:49:48 +01:00
parent 4a9e59da20
commit e00e657c1e
1 changed files with 44 additions and 0 deletions
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seqlock-fix-seqlock_write_unlock_impl-function.patch Normal file
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From 96e00e040cd8ae23cebf183cf3a8dc9cf1f6149d Mon Sep 17 00:00:00 2001
From: Luc Michel <luc.michel@greensocs.com>
Date: Wed, 29 Jan 2020 15:49:48 +0100
Subject: [PATCH] seqlock: fix seqlock_write_unlock_impl function
MIME-Version: 1.0
Content-Type: text/plain; charset=UTF-8
Content-Transfer-Encoding: 8bit
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>
---
include/qemu/seqlock.h | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/include/qemu/seqlock.h b/include/qemu/seqlock.h
index fd408b7ec5..8b6b4ee4bb 100644
--- 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))
--
2.27.0