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> Message-Id: <20160930213106.20186-6-alex.ben...@linaro.org> Signed-off-by: Paolo Bonzini <pbonz...@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 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) -- 2.7.4