On Wed, Apr 25, 2012 at 06:26:40PM +0200, Jan Kara wrote: > On Wed 25-04-12 07:29:30, J. Bruce Fields wrote: > > On Wed, Apr 25, 2012 at 12:23:12AM +0200, Jan Kara wrote: > > > On Tue 24-04-12 15:52:36, J. Bruce Fields wrote: > > > > On Fri, Apr 20, 2012 at 01:15:17PM +0200, Jan Kara wrote: > > > > > On Wed 18-04-12 00:44:24, Al Viro wrote: > > > > > > On Tue, Apr 17, 2012 at 03:08:26PM -0700, Linus Torvalds wrote: > > > > > > > > Or I could increment that counter for all the conflicting operations and > > > > > > > > rely on it instead of the i_mutex. ?I was trying to avoid adding > > > > > > > > something like that (an inc, a dec, another error path) to every > > > > > > > > operation. ?And hoping to avoid adding another field to struct inode. > > > > > > > > Oh well. > > > > > > > > > > > > > > We could just say that we can do a double inode lock, but then > > > > > > > standardize on the order. And the only sane order is comparing inode > > > > > > > pointers, not inode numbers like ext4 apparently does. > > > > > > > > > > > > > > With a standard order, I don't think it would be at all wrong to just > > > > > > > take the inode lock on rename. > > > > > > > > > > > > In principle, yes, but have you tried to grep for i_mutex? Note that > > > > > > we have *another* place where multiple ->i_mutex might be held on > > > > > > non-directories (and unless I'm missing something, ext4 move_extent.c > > > > > > stuff doesn't play well with it): quota writes. Which can, AFAICS, > > > > > > happen while write(2) is holding ->i_mutex on a regular file. So > > > > > > it's not _that_ easy - we want something like "and quota file is goes > > > > > > last", since there we don't get to change the locking order - the first > > > > > > ->i_mutex is taken too far outside. > > > > > Hum, I think I could just do away with quota file i_mutex being special. > > > > > It's used for two purposes: > > > > > 1) When quota is being turned on/off, we want to set/clear inode immutable > > > > > flag, truncate page cache, etc. But we should be able push this locking > > > > > outside of quota locks. > > > > > 2) Inside filesystems when quota file is written to. Quota writes are > > > > > serialized by quota code anyway and noone else has any bussiness with quota > > > > > files (they are marked as immutable to avoid mistakes) so there i_mutex is > > > > > not really needed. > > > > > > > > Grepping for I_MUTEX_QUOTA shows hits in ext4, reiserfs, and gfs2. The > > > > former two are in code called from the quota code (through the > > > > ->quota_write method). But the gfs2 code appears to be called directly > > > > from gfs2's write code. > > > Ah, gfs2 doesn't use generic quota code so whatever it does is it's own > > > invention. For ext4 and reiserfs I could get rid of I_MUTEX_QUOTA as I > > > wrote. > > > > So, just the appended? > Yup, that's the easier part. We also use the mutex in quota code itself > (fs/quota/dquot.c). That's somewhat harder to solve but still relatively > simple. Yeah, OK, I stared at that part but wasn't completely sure what you meant to do there. --b. > > But unfortunately as long as that's left in gfs2 we're still stuck > > trying to order quota files after other files when we take two > > non-directory i_mutexes elsewhere. > As far as GFS2 is concerned, I'm not sure what it uses i_mutex in quota > code for. In any case it should be possible to replace that usage by some > GFS2 internal lock to get rid of the last usage of I_MUTEX_QUOTA... Stephen? -- To unsubscribe from this list: send the line "unsubscribe linux-fsdevel" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
