[PATCH 1/2] io_uring: clarify io_req_task_cancel() locking

Pavel Begunkov
2021-08-25T19:52:22Z

It's too easy to forget and misjudge about synchronisation in
io_req_task_cancel(), add a comment clarifying it.

Signed-off-by: Pavel Begunkov <asml.silence@gmail.com>
---
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 15728e63d6f9..712605fd04c2 100644
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -2138,7 +2138,7 @@ static void io_req_task_cancel(struct io_kiocb *req, bool *locked)
{
struct io_ring_ctx *ctx = req->ctx;

- /* ctx is guaranteed to stay alive while we hold uring_lock */
+ /* not needed for normal modes, but SQPOLL depends on it */
io_tw_lock(ctx, locked);
io_req_complete_failed(req, req->result);
}
@@ -2147,7 +2147,6 @@ static void io_req_task_submit(struct io_kiocb *req, bool *locked)
{
struct io_ring_ctx *ctx = req->ctx;

- /* ctx stays valid until unlock, even if we drop all ours ctx->refs */
io_tw_lock(ctx, locked);
/* req->task == current here, checking PF_EXITING is safe */
if (likely(!(req->task->flags & PF_EXITING)))
--
2.32.0