linux-kernel - Re: NFS lockdep lock misordering mmap_sem<->i_mutex

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]

Date:	Wed, 16 Dec 2009 08:09:51 -0500
From:	Trond Myklebust <trond.myklebust@....uio.no>
To:	Andi Kleen <andi@...stfloor.org>
Cc:	Al Viro <viro@...IV.linux.org.uk>,
	KOSAKI Motohiro <kosaki.motohiro@...fujitsu.com>,
	linux-kernel@...r.kernel.org
Subject: Re: NFS lockdep lock misordering mmap_sem<->i_mutex_key with
 2.6.32-git1

On Wed, 2009-12-16 at 01:53 +0100, Andi Kleen wrote: 
> > If you want to work around the problem rather than going for something
> 
> I am mostly interested in making the ugly warning on my systems
> go away, preferably without breaking anything in the process.
> Whatever works.
> 
> > like Peter's split up of the mmap() callback, then I'd suggest changing
> > to using nfs_revalidate_mapping_nolock() instead. The fact that we are
> > seeing these lock misordering warnings is proof that the call to
> > nfs_revalidate_mapping() is not always a no-op.
> 
> I would say the interesting question is if there is really a expectation
> that mmap does this kind of synchronization? 

Usually people who set the 'noac' mount flag will expect these syscalls
to act as synchronisation points.

Typically, their applications will be using some kind of locking scheme
that does not require POSIX or BSD locks to be set. For instance, they
may synchronise by means of a token passed through a socket (common in
MPI iirc).

> Why in mmap, not somewhere else?

We do the same thing in the read() and write() syscalls.

Cheers
  Trond

--
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/