On Sun, 25 Mar 2012 13:26:10 -0700 (PDT) Hugh Dickins <hughd@xxxxxxxxxx> wrote: > 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(). > > Now, there might or might not be reasons why ext4 or xfs ought to hold > i_mutex there for its own consistency, but it's beyond me to determine > that: let's assume they're correct without evidence to the contrary. > > Stabilizing i_size is not a reason: holepunching does not affect i_size > and is not affected by i_size (okay, ext4 still has the bug I reported > a couple of months ago, whereby its holepunching stops at i_size, > forgetting blocks fallocated beyond; but no doubt that will get fixed). > > And nothing that truncate_pagecache_range() does needs i_mutex: > neither the unmap_mapping_range() nor the truncate_inode_pages_range() > needs i_mutex. A year ago, yes, Miklos showed how unmap_mapping_range() > was relying on mutex serialization, and added an additional mutex for > that, which Peter was able to remove once he mutified i_mmap_lock. > > truncate_pagecache_range() is just a drop-in replacement for > truncate_inode_pages_range(), and has no different locking needs. Does anything prevent new pages from getting added to pagecache and perhaps faulted into VMAs after or during the execution of these functions? Also, I wonder what prevents pages in the range from being dirtied between ext4_ext_punch_hole()'s filemap_write_and_wait_range() and truncate_inode_pages_range(). -- 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>