On 8/31/20 3:58 AM, gregkh@xxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxx>. Here's a backport: >From 84f81565a00f353c503d5b5bd98c77625af73b60 Mon Sep 17 00:00:00 2001 From: Jens Axboe <axboe@xxxxxxxxx> 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@xxxxxxxxxxxxxxx # v5.7+ Reported-by: Benedikt Ames <wisp3rwind@xxxxxxxxx> Signed-off-by: Jens Axboe <axboe@xxxxxxxxx> --- 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); -- 2.28.0 -- Jens Axboe
