linux-kernel - Re: OFD locks and deadlock detection

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: <20140519102802.16dee141@tlielax.poochiereds.net>
Date:	Mon, 19 May 2014 10:28:02 -0400
From:	Jeff Layton <jlayton@...chiereds.net>
To:	"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com>
Cc:	"linux-man@...r.kernel.org" <linux-man@...r.kernel.org>,
	lkml <linux-kernel@...r.kernel.org>,
	Linux-Fsdevel <linux-fsdevel@...r.kernel.org>,
	Andy Lutomirski <luto@...capital.net>
Subject: Re: OFD locks and deadlock detection

On Mon, 19 May 2014 15:18:13 +0200
"Michael Kerrisk (man-pages)" <mtk.manpages@...il.com> wrote:

> Hi Jeff,
> 
> I just happened to notice :
> 
>     commit 57b65325fe34ec4c917bc4e555144b4a94d9e1f7
>     Author: Jeff Layton <jlayton@...hat.com>
>     Date:   Mon Feb 3 12:13:09 2014 -0500
> 
>         locks: skip deadlock detection on FL_FILE_PVT locks
> 
> And then this thread:
> 
>     http://thread.gmane.org/gmane.linux.file-systems/81318/focus=81327
>     From: Jeff Layton <jlayton <at> redhat.com>
>     Subject: [PATCH v5 13/14] locks: skip deadlock detection on FL_FILE_PVT locks
>     Date: 2014-01-09 14:19:46 GMT
> 
> I think it's pretty important to document that. All implementations
> of traditional process-associated (.k.a. "POSIX") locks that I've ever 
> come across do detect deadlocks, so it's important to note that OFD locks 
> do not.
> 
> I plan to add the following text to the fcntl(2) page:
> 
> [[
> In the current implementation,
> no deadlock detection is performed for open file description locks.
> (This contrasts with process-associated record locks,
> for which the kernel does perform deadlock detection.)
> ]]
> 
> Okay?
> 
> cheers,
> 
> Michael
> 
> 

(note: I'm no longer with Red Hat, so jlayton@...hat.com no longer works)

Sounds fine to me.

FWIW, the deadlock detection for process-associated record locks is
pretty worthless except in certain narrow circumstances.

At some point, we probably should have a discussion as to whether
deadlock detection is really something we want to keep. The current
implementation requires a global spinlock which has obvious
consequences for scalability.

Thanks,
-- 
Jeff Layton <jlayton@...chiereds.net>
--
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/