From 0d7bae69c574c5f25802f8a71252e7d66933a3ab Mon Sep 17 00:00:00 2001 From: Stefan Bühler Date: Fri, 19 Apr 2019 11:57:45 +0200 Subject: io_uring: fix race condition when sq threads goes sleeping MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8bit 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 Signed-off-by: Jens Axboe --- fs/io_uring.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/fs/io_uring.c b/fs/io_uring.c index 41e3a6f6a096..69910fd9ccca 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()) { -- cgit