io_uring/poll: don't poll a writer for a read side hangup

io_init_poll_iocb() adds EPOLLRDHUP to every poll, including the async
poll of a send that waits for buffer space. Once the peer has shut down
its sending side, the socket keeps reporting EPOLLRDHUP, so each re-arm
in __io_arm_poll_handler() finds a ready mask and the request is issued
again. The send still can't make progress, the request burns through
APOLL_MAX_RETRY in a few milliseconds and ends up in io-wq.

A send in io-wq blocks until the peer reads, but sendmsg and writev go
through ____sys_sendmsg() and sock_write_iter(), which turn O_NONBLOCK
into MSG_DONTWAIT, and the application gets -EAGAIN for a request that
never asked for a non-blocking send.

Only add EPOLLRDHUP for polls that want to read. A peer that stopped
sending is no event for a writer, and a poll that asks for it explicitly
still gets it.

Fixes: 464dca612bc6 ("io_uring: mask in error/nval/hangup consistently for poll")
Reported-by: Lukáš Lalinský <lukas@lalinsky.com>
Signed-off-by: Jens Axboe <axboe@kernel.dk>

0 files changed, 0 insertions, 0 deletions