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SubjectRe: [PATCH] sysfs: differentiate between locking links and non-links
On Wed, Feb 10, 2010 at 12:09:33PM +1100, Neil Brown wrote:
> Hi,
> I've just spent a while sorting out some lockdep complaints triggered
> by the recent addition of the "s_active" lockdep annotation in sysfs
> (commit 846f99749ab68bbc7f75c74fec305de675b1a1bf)
> Some of them are genuine and I have submitted a fix for those.
> Some are, I think, debatable and I get to that is a minute. I've
> submitted a fix for them anyway.
> But some are to my mind clearly bogus and I'm hoping that can be
> fixed by the change below (or similar).
> The 'bogus' ones are triggered by writing to a sysfs attribute file
> for which the handler tries to delete a symlink from sysfs.
> This appears to be a recursion on s_active as s_active is held while
> the handler runs and is again needed to effect the delete. However
> as the thing being deleted is a symlink, it is very clearly a
> different object to the thing triggering the delete, so there is no
> real loop.
> The following patch splits the lockdep context in two - one for
> symlink and one for everything else. This removes the apparent loop.
> (An example report can be seen in
> The "debatable" dependency loops happen when writing to one attribute
> causes a different attribute to be deleted. In my (md) case this can
> actually cause a deadlock as both the attributes take the same lock
> while the handler is running. This is because deleting the attribute
> will block until the all accesses of that attribute have completed (I
> think).
> However it should be possible to delete a name from sysfs while there
> are still accesses pending (it works for normal files!!). So if
> sysfs could be changed to simply unlink the file and leave deletion to
> happen when the refcount become zero it would certainly make my life
> a lot easier, and allow the removal of some ugly code from md.c.
> I don't know sysfs well enough to suggest a patch though.
> Thanks,
> NeilBrown
> commit 2e502cfe444b68f6ef6b8b2abe83b6112564095b
> Author: NeilBrown <>
> 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.
> Signed-off-by: NeilBrown <>

Nice patch, I'll queue it up for .34.


greg k-h

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