linux-kernel - Re: SLUB sysfs support

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Message-ID: <20071227235437.GI27894@ZenIV.linux.org.uk>
Date:	Thu, 27 Dec 2007 23:54:37 +0000
From:	Al Viro <viro@...IV.linux.org.uk>
To:	Christoph Lameter <clameter@....com>
Cc:	Theodore Tso <tytso@....edu>, Andi Kleen <andi@...stfloor.org>,
	Willy Tarreau <w@....eu>, Steven Rostedt <rostedt@...dmis.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Peter Zijlstra <a.p.zijlstra@...llo.nl>,
	LKML <linux-kernel@...r.kernel.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Christoph Hellwig <hch@...radead.org>,
	"Rafael J. Wysocki" <rjw@...k.pl>
Subject: Re: SLUB sysfs support

On Thu, Dec 27, 2007 at 03:22:28PM -0800, Christoph Lameter wrote:
> > a) remove symlink when slab goes away
> 
> Ok. Need to think about how to code that.

Huh?  Just call it from kmem_cache_destroy(); what business does that symlink
have being around after that point?

> > b) instead of kfree() in slab removal do kobject_put() if you have sysfs stuff
> 
> Hmmmm.... Okay. Patch follows but its strange to do a kobject_put after a 
> kobject_del().

kobject_del() undoes the effect of kobject_add().  And then you are left
with the refcount you had before kobject_add(), i.e. from kobject_init().

Think of it that way: kobject refcount controls the lifetime of structure
the sucker's embedded into.  Depending on kobject methods, you might
be unable to do cleanup of non-kobject parts of that animal until after
kobject_del().  IOW, you _can't_ have kobject_del() dropping the (hopefully)
final reference to kobject - only the caller knows what might have to be
done in between.
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