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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

29
fs/btrfs/file.c
View File

@@ -1660,8 +1660,9 @@ static noinline ssize_t __btrfs_buffered_write(struct file *file,
reserve_bytes);
if (ret) {
if (!only_release_metadata)
btrfs_free_reserved_data_space(inode, pos,
write_bytes);
btrfs_free_reserved_data_space(inode,
data_reserved, pos,
write_bytes);
else
btrfs_end_write_no_snapshoting(root);
break;
@@ -1743,8 +1744,9 @@ again:
__pos = round_down(pos,
fs_info->sectorsize) +
(dirty_pages << PAGE_SHIFT);
btrfs_delalloc_release_space(inode, __pos,
release_bytes);
btrfs_delalloc_release_space(inode,
data_reserved, __pos,
release_bytes);
}
}
@@ -1799,9 +1801,9 @@ again:
btrfs_delalloc_release_metadata(BTRFS_I(inode),
release_bytes);
} else {
btrfs_delalloc_release_space(inode,
round_down(pos, fs_info->sectorsize),
release_bytes);
btrfs_delalloc_release_space(inode, data_reserved,
round_down(pos, fs_info->sectorsize),
release_bytes);
}
}
@@ -2918,8 +2920,8 @@ static long btrfs_fallocate(struct file *file, int mode,
* range, free reserved data space first, otherwise
* it'll result in false ENOSPC error.
*/
btrfs_free_reserved_data_space(inode, cur_offset,
last_byte - cur_offset);
btrfs_free_reserved_data_space(inode, data_reserved,
cur_offset, last_byte - cur_offset);
}
free_extent_map(em);
cur_offset = last_byte;
@@ -2938,8 +2940,9 @@ static long btrfs_fallocate(struct file *file, int mode,
range->len, i_blocksize(inode),
offset + len, &alloc_hint);
else
btrfs_free_reserved_data_space(inode, range->start,
range->len);
btrfs_free_reserved_data_space(inode,
data_reserved, range->start,
range->len);
list_del(&range->list);
kfree(range);
}
@@ -2977,8 +2980,8 @@ out:
inode_unlock(inode);
/* Let go of our reservation. */
if (ret != 0)
btrfs_free_reserved_data_space(inode, alloc_start,
alloc_end - cur_offset);
btrfs_free_reserved_data_space(inode, data_reserved,
alloc_start, alloc_end - cur_offset);
extent_changeset_free(data_reserved);
return ret;
}