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Btrfs: deal with short returns from copy_from_user

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When copy_from_user is only able to copy some of the bytes we requested,
we may end up creating a partially up to date page.  To avoid garbage in
the page, we need to treat a partial copy as a zero length copy.

This makes the rest of the file_write code drop the page and
retry the whole copy instead of marking the partially up to
date page as dirty.

Signed-off-by: Chris Mason <chris.mason@oracle.com>
cc: stable@kernel.org
This commit is contained in:
Chris Mason 2011-03-07 11:10:24 -05:00
parent b1bf862e9d
commit 31339acd07
1 changed files with 13 additions and 0 deletions
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13
fs/btrfs/file.c
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@ -69,6 +69,19 @@ static noinline int btrfs_copy_from_user(loff_t pos, int num_pages,
/* Flush processor's dcache for this page */ /* Flush processor's dcache for this page */
flush_dcache_page(page); flush_dcache_page(page);
/*
* if we get a partial write, we can end up with
* partially up to date pages. These add
* a lot of complexity, so make sure they don't
* happen by forcing this copy to be retried.
*
* The rest of the btrfs_file_write code will fall
* back to page at a time copies after we return 0.
*/
if (!PageUptodate(page) && copied < count)
copied = 0;
iov_iter_advance(i, copied); iov_iter_advance(i, copied);
write_bytes -= copied; write_bytes -= copied;
total_copied += copied; total_copied += copied;