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

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Date:	Wed, 10 Feb 2010 11:14:13 +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 11:05 AM, David Rientjes <rientjes@...gle.com> wrote:
> On Wed, 10 Feb 2010, Américo Wang wrote:
>
>> > 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.
>>
>
> You should be able to reuse Neil's sysfs_dirent_init_lockdep(sd, type) to
> seperate the lock classes for the sd getting pinned in
> sysfs_get_active_two() from sysfs_deactivate(), although using subclasses
> would probably be optimal since there is a clear parent -> child relationship.

Yeah, basically, my fix is also adding a separate lockdep class, but
at a different
level. I will send the fix as soon as I finish it.

Thanks.
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