On 8/31/20 3:58 AM, gregkh@linuxfoundation.org wrote:

The patch below does not apply to the 5.8-stable tree. If someone wants it applied there, or to any other stable or longterm tree, then please email the backport, including the original git commit id to stable@vger.kernel.org.

Here's a backport:

From 84f81565a00f353c503d5b5bd98c77625af73b60 Mon Sep 17 00:00:00 2001

From: Jens Axboe axboe@kernel.dk Date: Tue, 25 Aug 2020 12:27:50 -0600 Subject: [PATCH 2/3] 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 --- fs/io_uring.c | 10 +++++++++- 1 file changed, 9 insertions(+), 1 deletion(-)

diff --git a/fs/io_uring.c b/fs/io_uring.c index c384caad6466..2b7018456091 100644 --- a/fs/io_uring.c +++ b/fs/io_uring.c @@ -4503,12 +4503,20 @@ 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_MUST_PUNT | 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);