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. --b. -- 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
