io_uring: signal registered eventfd to process deferred task work
authorDylan Yudaken <dylany@fb.com>
Tue, 30 Aug 2022 12:50:12 +0000 (05:50 -0700)
committerJens Axboe <axboe@kernel.dk>
Wed, 21 Sep 2022 16:30:42 +0000 (10:30 -0600)
commit21a091b970cdbcf3e8ff829234b51be6f9192766
tree5f1b5bb144929d86300b1ed0732c60d645be9c26
parentd8e9214f119db5697382c63a62790a4afb5d00cd
io_uring: signal registered eventfd to process deferred task work

Some workloads rely on a registered eventfd (via
io_uring_register_eventfd(3)) in order to wake up and process the
io_uring.

In the case of a ring setup with IORING_SETUP_DEFER_TASKRUN, that eventfd
also needs to be signalled when there are tasks to run.

This changes an old behaviour which assumed 1 eventfd signal implied at
least 1 CQE, however only when this new flag is set (and so old users will
not notice). This should be expected with the IORING_SETUP_DEFER_TASKRUN
flag as it is not guaranteed that every task will result in a CQE.

Signed-off-by: Dylan Yudaken <dylany@fb.com>
Link: https://lore.kernel.org/r/20220830125013.570060-7-dylany@fb.com
[axboe: fold in call_rcu() serialization fix]
Signed-off-by: Jens Axboe <axboe@kernel.dk>
include/linux/io_uring_types.h
io_uring/io_uring.c