io_uring: retry poll if we got woken with non-matching mask

If we get woken and the poll doesn't match our mask, re-add the task
to the poll waitqueue and try again instead of completing the request
with a mask of 0.

Reported-by: Dan Melnic <dmm@fb.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 1064507..8ad4a15 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4412,8 +4412,20 @@ static void io_poll_complete(struct io_kiocb *req, __poll_t mask, int error)
 static void io_poll_task_handler(struct io_kiocb *req, struct io_kiocb **nxt)
 {
        struct io_ring_ctx *ctx = req->ctx;
+       struct io_poll_iocb *poll = &req->poll;
+
+       if (!req->result && !READ_ONCE(poll->canceled)) {
+               struct poll_table_struct pt = { ._key = poll->events };
+
+               req->result = vfs_poll(req->file, &pt) & poll->events;
+       }
 
        spin_lock_irq(&ctx->completion_lock);
+       if (!req->result && !READ_ONCE(poll->canceled)) {
+               add_wait_queue(poll->head, &poll->wait);
+               spin_unlock_irq(&ctx->completion_lock);
+               return;
+       }
        hash_del(&req->hash_node);
        io_poll_complete(req, req->result, 0);
        req->flags |= REQ_F_COMP_LOCKED;