Messages in this thread | | | Subject | Re: [PATCH] sysfs: differentiate between locking links and non-links | From | (Eric W. Biederman) | Date | Thu, 11 Feb 2010 14:47:57 -0800 |
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Greg KH <gregkh@suse.de> writes:
> On Thu, Feb 11, 2010 at 01:42:10PM -0800, Eric W. Biederman wrote: >> 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. > > Ugh, why not? > > Neil, care to fix this up?
#ifdef CONFIG_DEBUG_LOCK_ALLOC -#define sysfs_dirent_init_lockdep(sd) \ +#define sysfs_dirent_init_lockdep(sd, type) \ do { \ static struct lock_class_key __key; \ \ - lockdep_init_map(&sd->dep_map, "s_active", &__key, 0); \ + lockdep_init_map(&sd->dep_map, "s_active_" type, &__key, 0); \ } while(0) #else #define sysfs_dirent_init_lockdep(sd) do {} while(0) ^^^^
Eric
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