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SubjectRe: OFD locks and deadlock detection
On Mon, 19 May 2014 15:18:13 +0200
"Michael Kerrisk (man-pages)" <mtk.manpages@gmail.com> wrote:

> Hi Jeff,
>
> I just happened to notice :
>
> commit 57b65325fe34ec4c917bc4e555144b4a94d9e1f7
> Author: Jeff Layton <jlayton@redhat.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@redhat.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@poochiereds.net>


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