linux-kernel - Re: [PATCH] scsi: target: Fix recursive locking in __configfs_open

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Message-ID: <20260121175136.2ku57xskhwwg7syz@inspiron>
Date: Wed, 21 Jan 2026 23:21:36 +0530
From: Prithvi <activprithvi@...il.com>
To: Bart Van Assche <bvanassche@....org>
Cc: martin.petersen@...cle.com, linux-scsi@...r.kernel.org,
	target-devel@...r.kernel.org, linux-kernel@...r.kernel.org,
	hch@....de, jlbec@...lplan.org, linux-fsdevel@...r.kernel.org,
	linux-kernel-mentees@...ts.linux.dev, skhan@...uxfoundation.org,
	david.hunter.linux@...il.com, khalid@...nel.org,
	syzbot+f6e8174215573a84b797@...kaller.appspotmail.com,
	stable@...r.kernel.org
Subject: Re: [PATCH] scsi: target: Fix recursive locking in
 __configfs_open_file()

On Tue, Jan 20, 2026 at 05:48:16AM -0800, Bart Van Assche wrote:
> On 1/19/26 10:50 AM, Prithvi wrote:
> >   Possible unsafe locking scenario:
> > 
> >         CPU0
> >         ----
> >    lock(&p->frag_sem);
> >    lock(&p->frag_sem);
> The least intrusive way to suppress this type of lockdep complaints is
> by using lockdep_register_key() and lockdep_unregister_key().
> 
> Thanks,
> 
> Bart.

Hello Bart,

I tried using lockdep_register_key() and lockdep_unregister_key() for the
frag_sem lock, however it stil gives the possible recursive locking
warning. Here is the patch and the bug report from its test:

https://lore.kernel.org/all/6767d8ea.050a0220.226966.0021.GAE@google.com/T/#m3203ceddf3423b7116ba9225d182771608f93a6f

Would using down_read_nested() and subclasses be a better option here?

I also checked out some documentation regarding it and learnt that to use
the _nested() form, the hierarchy among the locks should be mapped
accurately; however, IIUC, there isn't any hierarchy between the locks in
this case, is this right?

Apologies if I am missing something obvious here, and thanks for your 
time and guidance.

Best Regards,
Prithvi