io_uring: hold uring_lock while completing failed polled io in io_wq_submit_work()

BugLink: https://bugs.launchpad.net/bugs/1910111
commit c07e6719511e77c4b289f62bfe96423eb6ea061d upstream.

io_iopoll_complete() does not hold completion_lock to complete polled io,
so in io_wq_submit_work(), we can not call io_req_complete() directly, to
complete polled io, otherwise there maybe concurrent access to cqring,
defer_list, etc, which is not safe. Commit dad1b1242fd5 ("io_uring: always
let io_iopoll_complete() complete polled io") has fixed this issue, but
Pavel reported that IOPOLL apart from rw can do buf reg/unreg requests(
IORING_OP_PROVIDE_BUFFERS or IORING_OP_REMOVE_BUFFERS), so the fix is not
good.

Given that io_iopoll_complete() is always called under uring_lock, so here
for polled io, we can also get uring_lock to fix this issue.

Fixes: dad1b1242fd5 ("io_uring: always let io_iopoll_complete() complete polled io")
Cc: <stable@vger.kernel.org> # 5.5+
Signed-off-by: Xiaoguang Wang <xiaoguang.wang@linux.alibaba.com>
Reviewed-by: Pavel Begunkov <asml.silence@gmail.com>
[axboe: don't deref 'req' after completing it']
Signed-off-by: Jens Axboe <axboe@kernel.dk>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Paolo Pisati <paolo.pisati@canonical.com>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 797874f215b1a3891d7a8ab6d086e06a0b2f1036..c47912104cfd358db5ae90b96bf6dfce049d03b9 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -6081,19 +6081,28 @@ static struct io_wq_work *io_wq_submit_work(struct io_wq_work *work)
        }
 
        if (ret) {
+               struct io_ring_ctx *lock_ctx = NULL;
+
+               if (req->ctx->flags & IORING_SETUP_IOPOLL)
+                       lock_ctx = req->ctx;
+
                /*
-                * io_iopoll_complete() does not hold completion_lock to complete
-                * polled io, so here for polled io, just mark it done and still let
-                * io_iopoll_complete() complete it.
+                * io_iopoll_complete() does not hold completion_lock to
+                * complete polled io, so here for polled io, we can not call
+                * io_req_complete() directly, otherwise there maybe concurrent
+                * access to cqring, defer_list, etc, which is not safe. Given
+                * that io_iopoll_complete() is always called under uring_lock,
+                * so here for polled io, we also get uring_lock to complete
+                * it.
                 */
-               if (req->ctx->flags & IORING_SETUP_IOPOLL) {
-                       struct kiocb *kiocb = &req->rw.kiocb;
+               if (lock_ctx)
+                       mutex_lock(&lock_ctx->uring_lock);
 
-                       kiocb_done(kiocb, ret, NULL);
-               } else {
-                       req_set_fail_links(req);
-                       io_req_complete(req, ret);
-               }
+               req_set_fail_links(req);
+               io_req_complete(req, ret);
+
+               if (lock_ctx)
+                       mutex_unlock(&lock_ctx->uring_lock);
        }
 
        return io_steal_work(req);