On Sun, Mar 25, 2012 at 01:26:10PM -0700, Hugh Dickins wrote: > On Fri, 23 Mar 2012, Andrew Morton wrote: > > On Fri, 23 Mar 2012 14:14:54 -0700 (PDT) > > Hugh Dickins <hughd@xxxxxxxxxx> wrote: > > > On Fri, 23 Mar 2012, Andrew Morton wrote: > > > > > > > > --- a/mm/truncate.c~mm-for-fs-add-truncate_pagecache_range-fix > > > > +++ a/mm/truncate.c > > > > @@ -639,6 +639,9 @@ int vmtruncate_range(struct inode *inode > > > > * with on-disk format, and the filesystem would not have to deal with > > > > * situations such as writepage being called for a page that has already > > > > * had its underlying blocks deallocated. > > > > + * > > > > + * Must be called with inode->i_mapping->i_mutex held. > > > > > > You catch me offguard: I forget whether that's an absolute requirement or > > > just commonly the case. What do the other interfaces in truncate.c say ?-) > > > > i_mutex is generally required, to stabilise i_size. > > Sorry for being quarrelsome, but I do want to Nak your followup "fix". > > Building a test kernel quickly told me that inode->i_mapping->i_mutex > doesn't exist, of course it's inode->i_mutex. > > Then running the test kernel quickly told me that neither ext4 nor xfs > (I didn't try ocfs2) holds inode->i_mutex where holepunching calls > truncate_inode_pages_range(). Just for completeness: ocfs2 holds i_mutex around the entire ocfs2_change_file_space() call, which can do hole punching and unwritten extent allocation (it is a clone of xfs_change_file_space()). xfs itself seems hold its own idea of a shared lock while doing the work and an exclusive lock around the transaction join. I'm not clear enough about xfs to say how this compares or even if I read it right. But ocfs2 uses an allocation sem to protect allocation changes, including i_size, so perhaps i_mutex isn't strictly necessary. I don't think we contend enough here to try hard to remove it :-) Joel -- "The question of whether computers can think is just like the question of whether submarines can swim." - Edsger W. Dijkstra http://www.jlbec.org/ jlbec@xxxxxxxxxxxx -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Fight unfair telecom internet charges in Canada: sign http://stopthemeter.ca/ Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>