On 09/22/2016 03:13 AM, Alex Bennée wrote:
From: Paolo Bonzini <pbonz...@redhat.com>

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 <alex.ben...@linaro.org>
Signed-off-by: Paolo Bonzini <pbonz...@redhat.com>
Signed-off-by: Alex Bennée <alex.ben...@linaro.org>
 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);

The read side isn't using a atomic_read right here.

This appears to be tsan silliness to me.


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