linux-kernel - Re: [PATCH] netfs: Fix lockdep warning from taking sb_writers whilst holding mmap

lists.openwall.net		lists / announce owl-users owl-dev john-users john-dev passwdqc-users yescrypt popa3d-users / oss-security kernel-hardening musl sabotage tlsify passwords / crypt-dev xvendor / Bugtraq Full-Disclosure linux-kernel linux-netdev linux-ext4 linux-hardening linux-cve-announce PHC
Open Source and information security mailing list archives

Hash Suite: Windows password security audit tool. GUI, reports in PDF.

[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]

Message-ID: <Ya9eDiFCE2fO7K/S@casper.infradead.org>
Date:   Tue, 7 Dec 2021 13:13:50 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     David Howells <dhowells@...hat.com>
Cc:     jack@...e.cz, jlayton@...nel.org, linux-cachefs@...hat.com,
        linux-fsdevel@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] netfs: Fix lockdep warning from taking sb_writers whilst
 holding mmap_lock

On Tue, Dec 07, 2021 at 11:19:35AM +0000, David Howells wrote:
> Taking sb_writers whilst holding mmap_lock isn't allowed and will result in
> a lockdep warning like that below.  The problem comes from cachefiles
> needing to take the sb_writers lock in order to do a write to the cache,
> but being asked to do this by netfslib called from readpage, readahead or
> write_begin[1].

Isn't it taking sb_writers _on a different filesystem_?  So there's not
a real deadlock here, just a need to tell lockdep that this is a
different subclass of lock?