linux-kernel - Re: [PATCH 1/8] lockdep: fix recursive read lock validation

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: <e2e108260804290803u75764b56t1c475a6d186aca8d@mail.gmail.com>
Date:	Tue, 29 Apr 2008 17:03:38 +0200
From:	"Bart Van Assche" <bart.vanassche@...il.com>
To:	"Peter Zijlstra" <a.p.zijlstra@...llo.nl>
Cc:	ego@...ibm.com, linux-kernel@...r.kernel.org,
	"Zdenek Kabelac" <zdenek.kabelac@...il.com>,
	"Oleg Nesterov" <oleg@...sign.ru>,
	"Heiko Carstens" <heiko.carstens@...ibm.com>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	"Andrew Morton" <akpm@...ux-foundation.org>,
	"Ingo Molnar" <mingo@...e.hu>,
	"Srivatsa Vaddagiri" <vatsa@...ibm.com>
Subject: Re: [PATCH 1/8] lockdep: fix recursive read lock validation

On Tue, Apr 29, 2008 at 4:57 PM, Peter Zijlstra <a.p.zijlstra@...llo.nl> wrote:
>
> On Tue, 2008-04-29 at 15:16 +0200, Bart Van Assche wrote:
>  > On Tue, Apr 29, 2008 at 2:57 PM, Gautham R Shenoy <ego@...ibm.com> wrote:
>  > > Subject: lockdep: fix recursive read lock validation
>  > >  This means that the following sequence is now invalid, whereas previously
>  > >  it was considered valid:
>  > >
>  > >   rlock(a); rlock(b); runlock(b); runlock(a)
>  > >   rlock(b); rlock(a);
>  >
>  > Why are you marking this sequence as invalid ? Although it can be
>  > debated whether it is good programming practice to be inconsistent
>  > about the order of read-locking, the above sequence can't be involved
>  > in a deadlock.
>
>  Not for pure read locks, but when you add write locks to it, it does get
>  deadlocky. Lockdep does not keep separate chains for read and write
>  locks.

Nesting writer locks inside reader locks is always a bad idea. So
please come up with an example of how varying the reader lock nesting
order can trigger a deadlock (when no writer locks are nested inside
reader locks and nested writer locks are always nested in the same
order).

Bart.
--
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@...r.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/