From: Nilay Shroff <nilay@linux.ibm.com>
To: Cen Zhang <zzzccc427@gmail.com>, Jens Axboe <axboe@kernel.dk>,
Keith Busch <kbusch@kernel.org>,
Johannes Thumshirn <johannes.thumshirn@wdc.com>,
Chaitanya Kulkarni <kch@nvidia.com>,
Damien Le Moal <dlemoal@kernel.org>,
Genjian Zhang <zhanggenjian@kylinos.cn>,
Hans Holmberg <hans.holmberg@wdc.com>,
Kees Cook <kees@kernel.org>, Matthew Wilcox <willy@infradead.org>,
Christophe JAILLET <christophe.jaillet@wanadoo.fr>,
Kyungchan Koh <kkc6196@fb.com>, Shaohua Li <shli@fb.com>
Cc: linux-block@vger.kernel.org, linux-kernel@vger.kernel.org,
baijiaju1990@gmail.com
Subject: Re: [PATCH] null_blk: cancel bw_timer on add-device error unwind
Date: Wed, 24 Jun 2026 19:51:10 +0530 [thread overview]
Message-ID: <f7919c52-1217-4a64-9e89-d03b70f49d65@linux.ibm.com> (raw)
In-Reply-To: <20260624071825.357098-1-zzzccc427@gmail.com>
On 6/24/26 12:48 PM, Cen Zhang wrote:
> null_blk starts the bandwidth hrtimer before the later add_disk/device_add
> failure points. If setup fails after the timer is queued, the shared error
> unwind frees struct nullb without draining bw_timer, so the callback can
> run on freed owner state.
>
> The buggy scenario involves two paths, with each column showing the order
> within that path:
>
> null_add_dev() error unwind: nullb_bwtimer_fn() callback path:
> 1. Start bw_timer for a throttled 1. The hrtimer expires after the free.
> device. 2. nullb_bwtimer_fn() recovers the
> 2. Hit a later add_disk/device_add embedded owner.
> failure. 3. The callback reads nullb->dev and
> 3. Free struct nullb. nullb->q.
> 4. Release the remaining queue and 4. The stale owner storage is used
> disk resources. after free.
>
> Cancel bw_timer in the shared error unwind before put_disk() and the
> remaining frees. The normal delete path already uses the same
> hrtimer_cancel() drain.
Looks good to me.
Reviewed-by: Nilay Shroff <nilay@linux.ibm.com>
prev parent reply other threads:[~2026-06-24 14:21 UTC|newest]
Thread overview: 2+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-06-24 7:18 [PATCH] null_blk: cancel bw_timer on add-device error unwind Cen Zhang
2026-06-24 14:21 ` Nilay Shroff [this message]
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