| Message ID | 20190419095746.22894-2-source@stbuehler.de (mailing list archive) |
|---|---|
| State | Accepted, archived |
| Headers | show |
| Series | [v1,1/3] io_uring: fix race condition reading SQ entries | expand |
diff --git a/fs/io_uring.c b/fs/io_uring.c index 96863e4780b7..912b0b304d90 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -1865,7 +1865,8 @@ static int io_sq_thread(void *data) /* Tell userspace we may need a wakeup call */ ctx->sq_ring->flags |= IORING_SQ_NEED_WAKEUP; - smp_wmb(); + /* make sure to read SQ tail after writing flags */ + smp_mb(); if (!io_get_sqring(ctx, &sqes[0])) { if (kthread_should_stop()) {
Reading the SQ tail needs to come after setting IORING_SQ_NEED_WAKEUP in flags; there is no cheap barrier for ordering a store before a load, a full memory barrier is required. Userspace needs a full memory barrier between updating SQ tail and checking for the IORING_SQ_NEED_WAKEUP too. Signed-off-by: Stefan Bühler <source@stbuehler.de> --- fs/io_uring.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)