linux-kernel - Re: [PATCH v2 5/6] maple_tree: Update check_forking() and bench

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: <ZPoThAU9zoW2q/YR@casper.infradead.org>
Date:   Thu, 7 Sep 2023 19:16:36 +0100
From:   Matthew Wilcox <willy@...radead.org>
To:     "Liam R. Howlett" <Liam.Howlett@...cle.com>,
        Peng Zhang <zhangpeng.00@...edance.com>,
        kernel test robot <oliver.sang@...el.com>,
        oe-lkp@...ts.linux.dev, lkp@...el.com,
        maple-tree@...ts.infradead.org, linux-mm@...ck.org, corbet@....net,
        akpm@...ux-foundation.org, brauner@...nel.org, surenb@...gle.com,
        michael.christie@...cle.com, peterz@...radead.org,
        mathieu.desnoyers@...icios.com, npiggin@...il.com,
        avagin@...il.com, linux-doc@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [PATCH v2 5/6] maple_tree: Update check_forking() and
 bench_forking()

On Thu, Sep 07, 2023 at 02:03:01PM -0400, Liam R. Howlett wrote:
> > >  WARNING: possible recursive locking detected
> > >  6.5.0-rc4-00632-g2730245bd6b1 #1 Tainted: G                TN
> > >  --------------------------------------------
> > >  swapper/1 is trying to acquire lock:
> > > ffffffff86485058 (&mt->ma_lock){+.+.}-{2:2}, at: check_forking (include/linux/spinlock.h:? lib/test_maple_tree.c:1854)
> > > 
> > >  but task is already holding lock:
> > >  ffff888110847a30 (&mt->ma_lock){+.+.}-{2:2}, at: check_forking (include/linux/spinlock.h:351 lib/test_maple_tree.c:1854)
> > Thanks for the test. I checked that these are two different locks, why
> > is this warning reported? Did I miss something?
> 
> I don't think you can nest spinlocks like this.  In my previous test I
> avoided nesting, but in your case we cannot avoid having both locks at
> the same time.
> 
> You can get around this by using an rwsemaphore, set the two trees as
> external and use down_write_nested(&lock2, SINGLE_DEPTH_NESTING) like
> the real fork.  Basically, switch the locking to exactly what fork does.

spin_lock_nested() exists.

You should probably both read through
Documentation/locking/lockdep-design.rst It's not the best user
documentation in the world, but it's what we have.