Re: FAILED: patch "[PATCH] block: nr_sects_write(): Disable preemption on seqcount write" failed to apply to 5.4-stable tree

[Sasha Levin <sashal@kernel.org>]

On Fri, Jun 19, 2020 at 03:43:39PM +0200, gregkh@linuxfoundation.org wrote:
>
>The patch below does not apply to the 5.4-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 15b81ce5abdc4b502aa31dff2d415b79d2349d2f Mon Sep 17 00:00:00 2001
>From: "Ahmed S. Darwish" <a.darwish@linutronix.de>
>Date: Wed, 3 Jun 2020 16:49:48 +0200
>Subject: [PATCH] block: nr_sects_write(): Disable preemption on seqcount write
>
>For optimized block readers not holding a mutex, the "number of sectors"
>64-bit value is protected from tearing on 32-bit architectures by a
>sequence counter.
>
>Disable preemption before entering that sequence counter's write side
>critical section. Otherwise, the read side can preempt the write side
>section and spin for the entire scheduler tick. If the reader belongs to
>a real-time scheduling class, it can spin forever and the kernel will
>livelock.
>
>Fixes: c83f6bf98dc1 ("block: add partition resize function to blkpg ioctl")
>Cc: <stable@vger.kernel.org>
>Signed-off-by: Ahmed S. Darwish <a.darwish@linutronix.de>
>Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
>Signed-off-by: Jens Axboe <axboe@kernel.dk>

part_nr_sects_write() was in include/linux/genhd.h before 581e26004a09
("block: move block layer internals out of include/linux/genhd.h").
Fixed and queued for all branched.

-- 
Thanks,
Sasha