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

    Thanks.
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