linux-kernel - Re: [PATCH] sysfs: differentiate between locking links and non-links

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Date:	Tue, 9 Feb 2010 17:21:48 -0800 (PST)
From:	David Rientjes <rientjes@...gle.com>
To:	Neil Brown <neilb@...e.de>
cc:	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Tejun Heo <tj@...nel.org>, Greg Kroah-Hartman <gregkh@...e.de>,
	Hugh Dickins <hugh.dickins@...cali.co.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] sysfs: differentiate  between locking links and
 non-links

On Wed, 10 Feb 2010, Neil Brown wrote:

> commit 2e502cfe444b68f6ef6b8b2abe83b6112564095b
> Author: NeilBrown <neilb@...e.de>
> Date:   Wed Feb 10 09:43:45 2010 +1100
> 
>     sysfs: differentiate  between locking links and non-links for sysfs
>     
>     symlinks and non-symlink is sysfs are very different.
>     A symlink can never be locked (active) while an attribute
>     modification routine is running.  So removing symlink from an
>     attribute 'store' routine should be permitted without any lockdep
>     warnings.
>     
>     So split the lockdep context for 's_active' in two, one for symlinks
>     and other for everything else.
>     

What happens for hard links such as writing to 
/sys/devices/block/xxx/queue/scheduler to change an I/O scheduler which 
requires sd->dep_map and sd->parent->dep_map in sysfs_get_active_two() to 
pin both?  The call to kobject_del() invokes the destruction that also 
requires sd->dep_map in sysfs_deactivate() because of the s_active lockdep 
annotation.

This is the scenario that is presented in
http://bugzilla.kernel.org/show_bug.cgi?id=15202.
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