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

[AmÃrico Wang]

On Wed, Feb 10, 2010 at 9:21 AM, David Rientjes <rientjes@xxxxxxxxxx> wrote:
> On Wed, 10 Feb 2010, Neil Brown wrote:
>
>> commit 2e502cfe444b68f6ef6b8b2abe83b6112564095b
>> Author: NeilBrown <neilb@xxxxxxx>
>> Date: Â Wed Feb 10 09:43:45 2010 +1100
>>
>> Â Â sysfs: differentiate Âbetween locking links and non-links for sysfs
>>
>> Â Â symlinks and non-symlink is sysfs are very different.
>> Â Â A symlink can never be locked (active) while an attribute
>> Â Â modification routine is running. ÂSo removing symlink from an
>> Â Â attribute 'store' routine should be permitted without any lockdep
>> Â Â warnings.
>>
>> Â Â So split the lockdep context for 's_active' in two, one for symlinks
>> Â Â 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? ÂThe 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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