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

[Greg KH <gregkh@linuxfoundation.org>]

On Sun, Jul 05, 2020 at 09:49:10AM -0400, Sasha Levin wrote:
> 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.

Great, thanks for adding that.

greg k-h