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. I really don't like how messy i_mutex had become these days. Right now I'm staring at 700-odd lines all over the place where it's taken/released and it's a wastebucket lock - used to protect random bits and scraps, with a lot of filesystems, etc. using it for purposes of their own ;-/ -- 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
