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