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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
Download patch file Download diff file Expand all files Collapse all files

12
fs/btrfs/extent-tree.c
View file

@ -4389,7 +4389,8 @@ void btrfs_free_reserved_data_space_noquota(struct inode *inode, u64 start,
* This one will handle the per-inode data rsv map for accurate reserved
* space framework.
*/
void btrfs_free_reserved_data_space(struct inode *inode, u64 start, u64 len)
void btrfs_free_reserved_data_space(struct inode *inode,
struct extent_changeset *reserved, u64 start, u64 len)
{
struct btrfs_root *root = BTRFS_I(inode)->root;
@ -4399,7 +4400,7 @@ void btrfs_free_reserved_data_space(struct inode *inode, u64 start, u64 len)
start = round_down(start, root->fs_info->sectorsize);
btrfs_free_reserved_data_space_noquota(inode, start, len);
btrfs_qgroup_free_data(inode, start, len);
btrfs_qgroup_free_data(inode, reserved, start, len);
}
static void force_metadata_allocation(struct btrfs_fs_info *info)
@ -6204,7 +6205,7 @@ int btrfs_delalloc_reserve_space(struct inode *inode,
return ret;
ret = btrfs_delalloc_reserve_metadata(BTRFS_I(inode), len);
if (ret < 0)
btrfs_free_reserved_data_space(inode, start, len);
btrfs_free_reserved_data_space(inode, *reserved, start, len);
return ret;
}
@ -6223,10 +6224,11 @@ int btrfs_delalloc_reserve_space(struct inode *inode,
* list if there are no delalloc bytes left.
* Also it will handle the qgroup reserved space.
*/
void btrfs_delalloc_release_space(struct inode *inode, u64 start, u64 len)
void btrfs_delalloc_release_space(struct inode *inode,
struct extent_changeset *reserved, u64 start, u64 len)
{
btrfs_delalloc_release_metadata(BTRFS_I(inode), len);
btrfs_free_reserved_data_space(inode, start, len);
btrfs_free_reserved_data_space(inode, reserved, start, len);
}
static int update_block_group(struct btrfs_trans_handle *trans,