From: Pavel Begunkov <asml.silence@gmail.com>
Date: Fri, 6 Mar 2020 22:15:22 +0000 (+0300)
Subject: io_uring: fix lockup with timeouts
X-Git-Tag: v5.10.7~3039^2~4
X-Git-Url: http://review.tizen.org/git/?a=commitdiff_plain;h=f0e20b8943509d81200cef5e30af2adfddba0f5c;p=platform%2Fkernel%2Flinux-rpi.git

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..c06082bb 100644
--- 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);
 	}