Re: FAILED: patch "[PATCH] io_uring: use signal based task_work running" failed to apply to 5.7-stable tree

[Sasha Levin <sashal@kernel.org>]

On Sun, Jul 05, 2020 at 01:26:56PM +0200, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 5.7-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>.
>
>thanks,
>
>greg k-h
>
>------------------ original commit in Linus's tree ------------------
>
>From ce593a6c480a22acba08795be313c0c6d49dd35d Mon Sep 17 00:00:00 2001
>From: Jens Axboe <axboe@kernel.dk>
>Date: Tue, 30 Jun 2020 12:39:05 -0600
>Subject: [PATCH] io_uring: use signal based task_work running
>
>Since 5.7, we've been using task_work to trigger async running of
>requests in the context of the original task. This generally works
>great, but there's a case where if the task is currently blocked
>in the kernel waiting on a condition to become true, it won't process
>task_work. Even though the task is woken, it just checks whatever
>condition it's waiting on, and goes back to sleep if it's still false.
>
>This is a problem if that very condition only becomes true when that
>task_work is run. An example of that is the task registering an eventfd
>with io_uring, and it's now blocked waiting on an eventfd read. That
>read could depend on a completion event, and that completion event
>won't get trigged until task_work has been run.
>
>Use the TWA_SIGNAL notification for task_work, so that we ensure that
>the task always runs the work when queued.
>
>Cc: stable@vger.kernel.org # v5.7
>Signed-off-by: Jens Axboe <axboe@kernel.dk>

This patch depends on e91b48162332 ("task_work: teach task_work_add() to
do signal_wake_up()"), I've queued both for 5.7.

-- 
Thanks,
Sasha