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Date: Wed, 10 Feb 2010 11:14:13 +0800
Message-ID: <2375c9f91002091914l6738a06eq5cba5f5fbf08976a@mail.gmail.com>
Subject: Re: [PATCH] sysfs: differentiate between locking links and non-links
From: =?UTF-8?Q?Am=C3=A9rico_Wang?= <xiyou.wangcong@gmail.com>
To: David Rientjes <rientjes@google.com>
Cc: Neil Brown <neilb@suse.de>, "Eric W. Biederman" <ebiederm@xmission.com>,
       Tejun Heo <tj@kernel.org>, Greg Kroah-Hartman <gregkh@suse.de>,
       Hugh Dickins <hugh.dickins@tiscali.co.uk>, linux-kernel@vger.kernel.org
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On Wed, Feb 10, 2010 at 11:05 AM, David Rientjes <rientjes@google.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.