Commit c933956d authored Feb 27, 2014 by Miao Xie Committed by Josef Bacik Mar 10, 2014

Btrfs: fix wrong lock range and write size in check_can_nocow()



The write range may not be sector-aligned, for example:

       |--------|--------|	<- write range, sector-unaligned, size: 2blocks
  |--------|--------|--------|  <- correct lock range, size: 3blocks

But according to the old code, we used the size of write range to calculate
the lock range directly, not considered the offset, we would get a wrong lock
range:

       |--------|--------|	<- write range, sector-unaligned, size: 2blocks
  |--------|--------|		<- wrong lock range, size: 2blocks

And besides that, the old code also had the same problem when calculating
the real write size. Correct them.

Signed-off-by: Miao Xie <miaox@cn.fujitsu.com>
Signed-off-by: Josef Bacik <jbacik@fb.com>

parent 9c9ca00b

fs/btrfs/file.c

+3 −2

Original line number	Diff line number	Diff line
		@@ -1411,7 +1411,7 @@ static noinline int check_can_nocow(struct inode *inode, loff_t pos,
		int ret;

		lockstart = round_down(pos, root->sectorsize);
		lockend = lockstart + round_up(*write_bytes, root->sectorsize) - 1;
		lockend = round_up(pos + *write_bytes, root->sectorsize) - 1;

		while (1) {
		lock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend);
		@@ -1434,7 +1434,8 @@ static noinline int check_can_nocow(struct inode *inode, loff_t pos,
		EXTENT_DIRTY \| EXTENT_DELALLOC \|
		EXTENT_DO_ACCOUNTING \| EXTENT_DEFRAG, 0, 0,
		NULL, GFP_NOFS);
		write_bytes = min_t(size_t, write_bytes, num_bytes);
		write_bytes = min_t(size_t, write_bytes ,
		num_bytes - pos + lockstart);
		}

		unlock_extent(&BTRFS_I(inode)->io_tree, lockstart, lockend);

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