It appears that there's a bug with this patch:
-------------------------------------------
commit 02fac1297eb3f471a27368271aadd285548297b0
Author: Allison Henderson <achender@xxxxxxxxxxxxxxxxxx>
Date: Tue Sep 6 21:53:01 2011 -0400
ext4: fix partial page writes
...
-------------------------------------------
Hugh Dickens found a bug with some nasty testing and lockdep that
crashed in ext4_da_write_end(), and after looking at the code with
him, it appears that the call to
ext4_discard_partial_page_buffers_no_lock() in this routine is
manipulating an unlocked, and possibly non-existent page:
-------------------------------------------
...
ret2 = generic_write_end(file, mapping, pos, len, copied,
page, fsdata);
page_len = PAGE_CACHE_SIZE -
((pos + copied - 1) & (PAGE_CACHE_SIZE - 1));
if (page_len > 0) {
ret = ext4_discard_partial_page_buffers_no_lock(handle,
inode, page, pos + copied - 1, page_len,
EXT4_DISCARD_PARTIAL_PG_ZERO_UNMAPPED);
}
...
-------------------------------------------
Note that generic_write_end() will unlock and release the page before
it returns.
I've no good answer for how to fix this properly, but I wanted to let
Allison know about this, if she hadn't already. I looked but didn't
see any related email on the linux-ext4 list for this problem.
Thanks,
Curt
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