Attention is currently required from: daniel, fixeria, jolly, laforge, pespin.

Hello Jenkins Builder, daniel, fixeria, jolly, laforge, osmith,

I'd like you to reexamine a change. Please visit

https://gerrit.osmocom.org/c/libosmocore/+/41671?usp=email

to look at the new patch set (#3).

The following approvals got outdated and were removed: Verified+1 by Jenkins Builder

Change subject: io_uring: RECVMSG_SENDMSG: Reset fd to blocking after osmo_fd_register() workaround ......................................................................

io_uring: RECVMSG_SENDMSG: Reset fd to blocking after osmo_fd_register() workaround

When IOFD_FLAG_NOTIFY_CONNECTED is requested by the user through osmo_iofd_notify_connected(), a write_cb(0, NULL) callback is done towards the user to notify the socket is connected.

In mode RECVMSG_SENDMSG, at least for SCTP sockets, according to comment in iofd_uring_register() (see also OS#5751) we cannot do the write(0) trick to get notifications, so instead we need to workaround by using a temporary osmo_fd to poll() for write status. To do so, we call osmo_fd_register(), which internally sets the fd as non-blocking (O_NONBLOCK). However, this is becomes an undesired behavior later on when connect happens and io_uring is used to recvmsg/sendmsg, since that could cause sqes to be answered with -EAGAIN cqes at the kernel isntead of keeping (blocking) them internally until the transaction can be resolved. This seems was a "desired" or "expected" behavior in older kernels according to public discussions/tickets, but it seeems it changed over time (see eg. GH#364 below).

In summary, the conclusion seems to be: try to avoid as much as possible mixing O_NONBLOCK with io_uring, as you may get totally unexpected/changing behavior.

Hence, avoid keeping O_NONBLOCK for those sockets when moving back from osmo_fd to io_uring.

See regarding related discussion on the expected behavior with io_uring and O_NONBLOCK: https://www.spinics.net/lists/io-uring/msg04058.html https://github.com/axboe/liburing/issues/364

Change-Id: Idba623730230bc049b827e51b058cd64d23b730f --- M src/core/osmo_io_uring.c 1 file changed, 22 insertions(+), 1 deletion(-)

git pull ssh://gerrit.osmocom.org:29418/libosmocore refs/changes/71/41671/3