io_uring: fix lockup with timeouts

There is a recipe to deadlock the kernel: submit a timeout sqe with a
linked_timeout (e.g.  test_single_link_timeout_ception() from liburing),
and SIGKILL the process.

Then, io_kill_timeouts() takes @ctx->completion_lock, but the timeout
isn't flagged with REQ_F_COMP_LOCKED, and will try to double grab it
during io_put_free() to cancel the linked timeout. Probably, the same
can happen with another io_kill_timeout() call site, that is
io_commit_cqring().

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 68050b6..c06082b 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -1000,6 +1000,7 @@ static void io_kill_timeout(struct io_kiocb *req)
        if (ret != -1) {
                atomic_inc(&req->ctx->cq_timeouts);
                list_del_init(&req->list);
+               req->flags |= REQ_F_COMP_LOCKED;
                io_cqring_fill_event(req, 0);
                io_put_req(req);
        }