Re: FAILED: patch "[PATCH] blkcg: make blkcg_print_stat() print stats only for online" failed to apply to 4.19-stable tree

[Sasha Levin <sashal@kernel.org>]

On Mon, Nov 11, 2019 at 07:12:24AM +0100, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 4.19-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 b0814361a25cba73a224548843ed92d8ea78715a Mon Sep 17 00:00:00 2001
>From: Tejun Heo <tj@kernel.org>
>Date: Tue, 5 Nov 2019 08:09:51 -0800
>Subject: [PATCH] blkcg: make blkcg_print_stat() print stats only for online
> blkgs
>
>blkcg_print_stat() iterates blkgs under RCU and doesn't test whether
>the blkg is online.  This can call into pd_stat_fn() on a pd which is
>still being initialized leading to an oops.
>
>The heaviest operation - recursively summing up rwstat counters - is
>already done while holding the queue_lock.  Expand queue_lock to cover
>the other operations and skip the blkg if it isn't online yet.  The
>online state is protected by both blkcg and queue locks, so this
>guarantees that only online blkgs are processed.
>
>Signed-off-by: Tejun Heo <tj@kernel.org>
>Reported-by: Roman Gushchin <guro@fb.com>
>Cc: Josef Bacik <jbacik@fb.com>
>Fixes: 903d23f0a354 ("blk-cgroup: allow controllers to output their own stats")
>Cc: stable@vger.kernel.org # v4.19+
>Signed-off-by: Jens Axboe <axboe@kernel.dk>

I've adjusted the patch for not having 0d945c1f966b ("block: remove the
queue_lock indirection") and queued it for 4.19.

-- 
Thanks,
Sasha