linux-kernel - Re: [PATCH] block: prevent deadlock in del

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Message-ID: <20250805120001.3990-1-hdanton@sina.com>
Date: Tue,  5 Aug 2025 19:59:59 +0800
From: Hillf Danton <hdanton@...a.com>
To: Yu Kuai <yukuai1@...weicloud.com>
Cc: Ujwal Kundur <ujwal.kundur@...il.com>,
	axboe@...nel.dk,
	ming.lei@...hat.com,
	linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	syzbot+2e9e529ac0b319316453@...kaller.appspotmail.com,
	"yukuai (C)" <yukuai3@...wei.com>
Subject: Re: [PATCH] block: prevent deadlock in del_gendisk()

On Mon, 4 Aug 2025 15:51:48 +0800 Yu Kuai wrote:
> 在 2025/08/03 21:41, Ujwal Kundur 写道:
> > A potential unsafe locking scenario presents itself when
> > mutex_lock(&disk->open_mutex) is called with reader's lock held on
> > update_nr_hwq_lock:
> >         CPU0                    CPU1
> >         ----                    ----
> > rlock(&set->update_nr_hwq_lock)
> >                                 lock(&nbd->config_lock);
> >                                 lock(&set->update_nr_hwq_lock);
> > lock(&disk->open_mutex)
> > 
> This problem is already fixed inside nbd by:
> 8b428f42f3ed ("nbd: fix lockdep deadlock warning")
> 
Deadlock still exists [1].

[1] https://lore.kernel.org/lkml/6891742c.050a0220.7f033.001a.GAE@google.com/