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. r~
