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