[PATCH 5.7 36/79] io_uring: fix lockup in io_fail_links()

Greg Kroah-Hartman
2020-08-10T15:24:01Z

From: Pavel Begunkov <asml.silence@gmail.com>

[ Upstream commit 4ae6dbd683860b9edc254ea8acf5e04b5ae242e5 ]

io_fail_links() doesn't consider REQ_F_COMP_LOCKED leading to nested
spin_lock(completion_lock) and lockup.

[ 197.680409] rcu: INFO: rcu_preempt detected expedited stalls on
CPUs/tasks: { 6-... } 18239 jiffies s: 1421 root: 0x40/.
[ 197.680411] rcu: blocking rcu_node structures:
[ 197.680412] Task dump for CPU 6:
[ 197.680413] link-timeout R running task 0 1669
1 0x8000008a
[ 197.680414] Call Trace:
[ 197.680420] ? io_req_find_next+0xa0/0x200
[ 197.680422] ? io_put_req_find_next+0x2a/0x50
[ 197.680423] ? io_poll_task_func+0xcf/0x140
[ 197.680425] ? task_work_run+0x67/0xa0
[ 197.680426] ? do_exit+0x35d/0xb70
[ 197.680429] ? syscall_trace_enter+0x187/0x2c0
[ 197.680430] ? do_group_exit+0x43/0xa0
[ 197.680448] ? __x64_sys_exit_group+0x18/0x20
[ 197.680450] ? do_syscall_64+0x52/0xa0
[ 197.680452] ? entry_SYSCALL_64_after_hwframe+0x44/0xa9

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Sasha Levin <sashal@kernel.org>
---
fs/io_uring.c | 3 +--
1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 4e09af1d5d223..fb9dc865c9eaa 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4260,10 +4260,9 @@ static void io_poll_task_handler(struct io_kiocb *req, struct io_kiocb **nxt)

hash_del(&req->hash_node);
io_poll_complete(req, req->result, 0);
- req->flags |= REQ_F_COMP_LOCKED;
- io_put_req_find_next(req, nxt);
spin_unlock_irq(&ctx->completion_lock);

+ io_put_req_find_next(req, nxt);
io_cqring_ev_posted(ctx);
}

--
2.25.1