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btrfs: qgroup: Fix qgroup reserved space underflow by only freeing reserved ranges

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[BUG]
For the following case, btrfs can underflow qgroup reserved space
at an error path:
(Page size 4K, function name without "btrfs_" prefix)

         Task A                  |             Task B
----------------------------------------------------------------------
Buffered_write [0, 2K)           |
|- check_data_free_space()       |
|  |- qgroup_reserve_data()      |
|     Range aligned to page      |
|     range [0, 4K)          <<< |
|     4K bytes reserved      <<< |
|- copy pages to page cache      |
                                 | Buffered_write [2K, 4K)
                                 | |- check_data_free_space()
                                 | |  |- qgroup_reserved_data()
                                 | |     Range alinged to page
                                 | |     range [0, 4K)
                                 | |     Already reserved by A <<<
                                 | |     0 bytes reserved      <<<
                                 | |- delalloc_reserve_metadata()
                                 | |  And it *FAILED* (Maybe EQUOTA)
                                 | |- free_reserved_data_space()
                                      |- qgroup_free_data()
                                         Range aligned to page range
                                         [0, 4K)
                                         Freeing 4K
(Special thanks to Chandan for the detailed report and analyse)

[CAUSE]
Above Task B is freeing reserved data range [0, 4K) which is actually
reserved by Task A.

And at writeback time, page dirty by Task A will go through writeback
routine, which will free 4K reserved data space at file extent insert
time, causing the qgroup underflow.

[FIX]
For btrfs_qgroup_free_data(), add @reserved parameter to only free
data ranges reserved by previous btrfs_qgroup_reserve_data().
So in above case, Task B will try to free 0 byte, so no underflow.

Reported-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Tested-by: Chandan Rajendra <chandan@linux.vnet.ibm.com>
Signed-off-by: David Sterba <dsterba@suse.com>
This commit is contained in:
Qu Wenruo
2017-02-27 15:10:39 +08:00
committed by David Sterba
parent 364ecf3651
commit bc42bda223
8 changed files with 117 additions and 46 deletions
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8
fs/btrfs/relocation.c
View File

@@ -3114,8 +3114,8 @@ int prealloc_file_extent_cluster(struct inode *inode,
lock_extent(&BTRFS_I(inode)->io_tree, start, end);
num_bytes = end + 1 - start;
if (cur_offset < start)
btrfs_free_reserved_data_space(inode, cur_offset,
start - cur_offset);
btrfs_free_reserved_data_space(inode, data_reserved,
cur_offset, start - cur_offset);
ret = btrfs_prealloc_file_range(inode, 0, start,
num_bytes, num_bytes,
end + 1, &alloc_hint);
@@ -3126,8 +3126,8 @@ int prealloc_file_extent_cluster(struct inode *inode,
nr++;
}
if (cur_offset < prealloc_end)
btrfs_free_reserved_data_space(inode, cur_offset,
prealloc_end + 1 - cur_offset);
btrfs_free_reserved_data_space(inode, data_reserved,
cur_offset, prealloc_end + 1 - cur_offset);
out:
inode_unlock(inode);
extent_changeset_free(data_reserved);