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io_uring: always do atomic put from iowq

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[ Upstream commit 390513642e ]

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.1743679736.git.asml.silence@gmail.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Pavel Begunkov 2025-04-03 12:29:30 +01:00 committed by Greg Kroah-Hartman
parent 7e9b836182
commit c5d4d10300
2 changed files with 8 additions and 1 deletions
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2
io_uring/io_uring.c
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@ -1917,7 +1917,7 @@ 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);

7
io_uring/refs.h
View File

@ -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)))