linux-kernel - Re: [PATCH] autofs4 - use simple_empty() for empty directory check

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Date:	Fri, 16 Nov 2012 17:34:15 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Ian Kent <ikent@...hat.com>,
	Kernel Mailing List <linux-kernel@...r.kernel.org>,
	autofs mailing list <autofs@...r.kernel.org>,
	linux-fsdevel <linux-fsdevel@...r.kernel.org>
Subject: Re: [PATCH] autofs4 - use simple_empty() for empty directory check

On Fri, Nov 16, 2012 at 08:43:28AM -0800, Linus Torvalds wrote:
> On Fri, Nov 16, 2012 at 8:36 AM, Ian Kent <ikent@...hat.com> wrote:
> >
> > Sure, are you recommending I alter the fs/libfs.c functions to add a
> > function that doesn't have the outer lock, and have simple_empty() call
> > that, then use it in autofs?
> 
> Yup. That's the standard pattern, although usually we *strive* to make
> the unlocked versions be static to the internal code, and then use
> them there for the various helpers. In your case that seems
> impossible, since you do depend on holding the d_lock in the caller
> after the tests. But at least we don't have to duplicate the code and
> have it in two unrelated places.
> 
> Al? Comments?

The thing is, I'm not convinced we really need ->d_lock held downstream.
E.g.  __autofs4_add_expiring() ought to be OK with just sbi->lookup_lock.
Not sure about the situation in autofs4_d_automount() - the thing is messy
as hell ;-/

Ian, do we really need that __simple_empty() variant in either caller?  What
is getting protected by ->d_lock after it and do we really need ->d_lock
continuously held for that?
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