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

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Message-ID: <2375c9f91002091756h132e81eava8575ffd4e3ad421@mail.gmail.com>
Date:	Wed, 10 Feb 2010 09:56:31 +0800
From:	Américo Wang <xiyou.wangcong@...il.com>
To:	David Rientjes <rientjes@...gle.com>
Cc:	Neil Brown <neilb@...e.de>,
	"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, Feb 10, 2010 at 9:21 AM, David Rientjes <rientjes@...gle.com> wrote:
> 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 not related with Neil's case at all.

The I/O scheduler switch case should be a bogus, I am working on
it. We have more similar cases of cpu hotplug. Trust me, I am working
on a fix to all of them, this is not as easy as you may think about.

Thanks.
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