From: Pavel Begunkov asml.silence@gmail.com
[ Upstream commit 390513642ee6763c7ada07f0a1470474986e6c1c ]
io_uring always switches requests to atomic refcounting for iowq execution before there is any parallilism by setting REQ_F_REFCOUNT, and the flag is not cleared until the request completes. That should be fine as long as the compiler doesn't make up a non existing value for the flags, however KCSAN still complains when the request owner changes oter flag bits:
BUG: KCSAN: data-race in io_req_task_cancel / io_wq_free_work ... read to 0xffff888117207448 of 8 bytes by task 3871 on cpu 0: req_ref_put_and_test io_uring/refs.h:22 [inline]
Skip REQ_F_REFCOUNT checks for iowq, we know it's set.
Reported-by: syzbot+903a2ad71fb3f1e47cf5@syzkaller.appspotmail.com Signed-off-by: Pavel Begunkov asml.silence@gmail.com Link: https://lore.kernel.org/r/d880bc27fb8c3209b54641be4ff6ac02b0e5789a.174367973... Signed-off-by: Jens Axboe axboe@kernel.dk Signed-off-by: Sasha Levin sashal@kernel.org --- io_uring/io_uring.c | 2 +- io_uring/refs.h | 7 +++++++ 2 files changed, 8 insertions(+), 1 deletion(-)
diff --git a/io_uring/io_uring.c b/io_uring/io_uring.c index cf28d29fffbf0..20b6a9ec9da70 100644 --- a/io_uring/io_uring.c +++ b/io_uring/io_uring.c @@ -1777,7 +1777,7 @@ struct io_wq_work *io_wq_free_work(struct io_wq_work *work) struct io_kiocb *req = container_of(work, struct io_kiocb, work); struct io_kiocb *nxt = NULL;
- if (req_ref_put_and_test(req)) { + if (req_ref_put_and_test_atomic(req)) { if (req->flags & IO_REQ_LINK_FLAGS) nxt = io_req_find_next(req); io_free_req(req); diff --git a/io_uring/refs.h b/io_uring/refs.h index 63982ead9f7da..0d928d87c4ed1 100644 --- a/io_uring/refs.h +++ b/io_uring/refs.h @@ -17,6 +17,13 @@ static inline bool req_ref_inc_not_zero(struct io_kiocb *req) return atomic_inc_not_zero(&req->refs); }
+static inline bool req_ref_put_and_test_atomic(struct io_kiocb *req) +{ + WARN_ON_ONCE(!(data_race(req->flags) & REQ_F_REFCOUNT)); + WARN_ON_ONCE(req_ref_zero_or_close_to_overflow(req)); + return atomic_dec_and_test(&req->refs); +} + static inline bool req_ref_put_and_test(struct io_kiocb *req) { if (likely(!(req->flags & REQ_F_REFCOUNT)))