Messages in this thread | | | Date | Sun, 25 Mar 2012 13:50:02 -0700 | From | Andrew Morton <> | Subject | Re: [PATCH] mm for fs: add truncate_pagecache_range |
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On Sun, 25 Mar 2012 13:26:10 -0700 (PDT) Hugh Dickins <hughd@google.com> 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().
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