On Sun, Jul 05, 2020 at 01:26:56PM +0200, gregkh@xxxxxxxxxxxxxxxxxxx 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@xxxxxxxxxxxxxxx>.
thanks,
greg k-h
------------------ original commit in Linus's tree ------------------
From ce593a6c480a22acba08795be313c0c6d49dd35d Mon Sep 17 00:00:00 2001
From: Jens Axboe <axboe@xxxxxxxxx>
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@xxxxxxxxxxxxxxx # v5.7
Signed-off-by: Jens Axboe <axboe@xxxxxxxxx>
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
