linux-kernel - Re: [PATCH] Wake up mandatory locks waiter on chmod (v2)

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Message-ID: <46EF7136.7080308@openvz.org>
Date:	Tue, 18 Sep 2007 10:33:26 +0400
From:	Pavel Emelyanov <xemul@...nvz.org>
To:	Trond Myklebust <trond.myklebust@....uio.no>
CC:	Andrew Morton <akpm@...l.org>,
	"J. Bruce Fields" <bfields@...ldses.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	devel@...nvz.org
Subject: Re: [PATCH] Wake up mandatory locks waiter on chmod (v2)

Trond Myklebust wrote:
> On Mon, 2007-09-17 at 18:16 +0400, Pavel Emelyanov wrote:
>> Trond Myklebust wrote:
>>> On Mon, 2007-09-17 at 12:13 +0400, Pavel Emelyanov wrote:
>>>> When the process is blocked on mandatory lock and someone changes 
>>>> the inode's permissions, so that the lock is no longer mandatory,
>>>> nobody wakes up the blocked process, but probably should.
>>> Please explain in more detail why we need this patch.
>> From "this fixes an OOPs/deadlock/leak" POV we do not. This is
>> just an attempt to make the locking code be more consistent and
>> clean.
> 
> Why do you think we get a deadlock or leak? AFAICS if the user turns off

I didn't' tell that.

> mandatory locks on the file, then the existing locks default back into
> advisory locks which use the same notification mechanism as the
> mandatory locks.

True.

> IOW: the process that is waiting in locks_mandatory_area() will be
> released as soon as the advisory lock is dropped. If that theory is
> broken in practice, then that is the bug that we need to fix. We neither
> want to add a load of locking crap to notify_change(), nor should we
> need to.

We have this for inotify already. Adding wakeup for mandatory lock
is not that bad.

Anyway - I noticed, that the system state can become not consistent
and proposed the way to fix it. If this inconsistency is not a big
deal, and nobody cares, than I'm fine with forgetting this patch, 
since I have no other arguments to protect it, but "this is just not
very nice without this patch".

> Cheers
>    Trond
> 
> 

Thanks,
Pavel
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