Messages in this thread | | | Subject | Re: [PATCH] sysfs: differentiate between locking links and non-links | From | (Eric W. Biederman) | Date | Thu, 11 Feb 2010 13:42:10 -0800 |
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Greg KH <gregkh@suse.de> writes:
> 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 >> http://bugzilla.kernel.org/show_bug.cgi?id=15142). >> >> 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 <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. >> >> Signed-off-by: NeilBrown <neilb@suse.de> > > Nice patch, I'll queue it up for .34.
Note the patch does not compile with lockdep disabled.
Eric
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