io_uring: don't use poll handler if file can't be nonblocking read/written

There's no point in using the poll handler if we can't do a nonblocking
IO attempt of the operation, since we'll need to go async anyway. In
fact this is actively harmful, as reading from eg pipes won't return 0
to indicate EOF.

Cc: stable@vger.kernel.org # v5.7+
Reported-by: Benedikt Ames <wisp3rwind@posteo.eu>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

diff --git a/fs/io_uring.c b/fs/io_uring.c
index 384df86..d151390 100644 (file)
--- a/fs/io_uring.c
+++ b/fs/io_uring.c
@@ -4889,12 +4889,20 @@ static bool io_arm_poll_handler(struct io_kiocb *req)
        struct async_poll *apoll;
        struct io_poll_table ipt;
        __poll_t mask, ret;
+       int rw;
 
        if (!req->file || !file_can_poll(req->file))
                return false;
        if (req->flags & REQ_F_POLLED)
                return false;
-       if (!def->pollin && !def->pollout)
+       if (def->pollin)
+               rw = READ;
+       else if (def->pollout)
+               rw = WRITE;
+       else
+               return false;
+       /* if we can't nonblock try, then no point in arming a poll handler */
+       if (!io_file_supports_async(req->file, rw))
                return false;
 
        apoll = kmalloc(sizeof(*apoll), GFP_ATOMIC);