Re: FAILED: patch "[PATCH] nbd: fix max number of supported devs" failed to apply to 4.14-stable tree

[Sasha Levin <sashal@kernel.org>]

On Tue, Oct 08, 2019 at 09:25:58AM +0200, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 4.14-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 e9e006f5fcf2bab59149cb38a48a4817c1b538b4 Mon Sep 17 00:00:00 2001
>From: Mike Christie <mchristi@redhat.com>
>Date: Sun, 4 Aug 2019 14:10:06 -0500
>Subject: [PATCH] nbd: fix max number of supported devs
>
>This fixes a bug added in 4.10 with commit:
>
>commit 9561a7ade0c205bc2ee035a2ac880478dcc1a024
>Author: Josef Bacik <jbacik@fb.com>
>Date:   Tue Nov 22 14:04:40 2016 -0500
>
>    nbd: add multi-connection support
>
>that limited the number of devices to 256. Before the patch we could
>create 1000s of devices, but the patch switched us from using our
>own thread to using a work queue which has a default limit of 256
>active works.
>
>The problem is that our recv_work function sits in a loop until
>disconnection but only handles IO for one connection. The work is
>started when the connection is started/restarted, but if we end up
>creating 257 or more connections, the queue_work call just queues
>connection257+'s recv_work and that waits for connection 1 - 256's
>recv_work to be disconnected and that work instance completing.
>
>Instead of reverting back to kthreads, this has us allocate a
>workqueue_struct per device, so we can block in the work.
>
>Cc: stable@vger.kernel.org
>Reviewed-by: Josef Bacik <josef@toxicpanda.com>
>Signed-off-by: Mike Christie <mchristi@redhat.com>
>Signed-off-by: Jens Axboe <axboe@kernel.dk>

I've queued up 553768d1169a4 ("nbd: fix crash when the blksize is zero")
and 2189c97cdbed6 ("block/ndb: add WQ_UNBOUND to the knbd-recv
workqueue") to resolve this on 4.14.

-- 
Thanks,
Sasha