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[Qemu-devel] [RFC 4/8] seqlock: use atomic writes for the sequence
From: |
Alex Bennée |
Subject: |
[Qemu-devel] [RFC 4/8] seqlock: use atomic writes for the sequence |
Date: |
Mon, 19 Sep 2016 16:51:35 +0100 |
From: Paolo Bonzini <address@hidden>
There is a data race if the sequence is written concurrently to the
read. In C11 this has undefined behavior. Use atomic_set; the
read side is already using atomic_read.
Reported-by: Alex Bennée <address@hidden>
Signed-off-by: Paolo Bonzini <address@hidden>
Signed-off-by: Alex Bennée <address@hidden>
---
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 2e2be4c..8dee11d 100644
--- a/include/qemu/seqlock.h
+++ b/include/qemu/seqlock.h
@@ -31,7 +31,7 @@ static inline void seqlock_init(QemuSeqLock *sl)
/* Lock out other writers and update the count. */
static inline void seqlock_write_begin(QemuSeqLock *sl)
{
- ++sl->sequence;
+ atomic_set(&sl->sequence, sl->sequence + 1);
/* Write sequence before updating other fields. */
smp_wmb();
@@ -42,7 +42,7 @@ static inline void seqlock_write_end(QemuSeqLock *sl)
/* Write other fields before finalizing sequence. */
smp_wmb();
- ++sl->sequence;
+ atomic_set(&sl->sequence, sl->sequence + 1);
}
static inline unsigned seqlock_read_begin(QemuSeqLock *sl)
--
2.9.3
[Qemu-devel] [RFC 3/8] new: blacklist.tsan, Alex Bennée, 2016/09/19
[Qemu-devel] [RFC 4/8] seqlock: use atomic writes for the sequence,
Alex Bennée <=
[Qemu-devel] [RFC 8/8] .travis.yml: add gcc sanitizer build, Alex Bennée, 2016/09/19
[Qemu-devel] [RFC 7/8] util/qht: atomically set b->hashes, Alex Bennée, 2016/09/19