linux-kernel - Re: [PATCH v2] proc/vmcore: fix possible deadlock on concurrent mmap and read

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: <20220125170900.472fdb649312e77a4a60d9da@linux-foundation.org>
Date:   Tue, 25 Jan 2022 17:09:00 -0800
From:   Andrew Morton <akpm@...ux-foundation.org>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-kernel@...r.kernel.org, kexec@...ts.infradead.org,
        linux-fsdevel@...r.kernel.org, linux-mm@...ck.org,
        Baoquan He <bhe@...hat.com>, Vivek Goyal <vgoyal@...hat.com>,
        Dave Young <dyoung@...hat.com>,
        "Paul E. McKenney" <paulmck@...nel.org>,
        Josh Triplett <josh@...htriplett.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Boqun Feng <boqun.feng@...il.com>
Subject: Re: [PATCH v2] proc/vmcore: fix possible deadlock on concurrent
 mmap and read

On Wed, 19 Jan 2022 20:34:17 +0100 David Hildenbrand <david@...hat.com> wrote:

> Lockdep noticed that there is chance for a deadlock if we have
> concurrent mmap, concurrent read, and the addition/removal of a
> callback.
> 
> As nicely explained by Boqun:
> 
> "
> Lockdep warned about the above sequences because rw_semaphore is a fair
> read-write lock, and the following can cause a deadlock:
> 
> 	TASK 1			TASK 2		TASK 3
> 	======			======		======
> 	down_write(mmap_lock);
> 				down_read(vmcore_cb_rwsem)
> 						down_write(vmcore_cb_rwsem); // blocked
> 	down_read(vmcore_cb_rwsem); // cannot get the lock because of the fairness
> 				down_read(mmap_lock); // blocked

I'm wondering about cc:stable.  It's hard to believe that this is
likely to be observed in real life.  But the ongoing reports of lockdep
splats will be irritating.