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Subject[PATCH 4.14 220/237] btrfs: fix bytes_may_use underflow in prealloc error condtition
Date
From: Josef Bacik <josef@toxicpanda.com>

commit b778cf962d71a0e737923d55d0432f3bd287258e upstream.

I hit the following warning while running my error injection stress
testing:

WARNING: CPU: 3 PID: 1453 at fs/btrfs/space-info.h:108 btrfs_free_reserved_data_space_noquota+0xfd/0x160 [btrfs]
RIP: 0010:btrfs_free_reserved_data_space_noquota+0xfd/0x160 [btrfs]
Call Trace:
btrfs_free_reserved_data_space+0x4f/0x70 [btrfs]
__btrfs_prealloc_file_range+0x378/0x470 [btrfs]
elfcorehdr_read+0x40/0x40
? elfcorehdr_read+0x40/0x40
? btrfs_commit_transaction+0xca/0xa50 [btrfs]
? dput+0xb4/0x2a0
? btrfs_log_dentry_safe+0x55/0x70 [btrfs]
? btrfs_sync_file+0x30e/0x420 [btrfs]
? do_fsync+0x38/0x70
? __x64_sys_fdatasync+0x13/0x20
? do_syscall_64+0x5b/0x1b0
? entry_SYSCALL_64_after_hwframe+0x44/0xa9

This happens if we fail to insert our reserved file extent. At this
point we've already converted our reservation from ->bytes_may_use to
->bytes_reserved. However once we break we will attempt to free
everything from [cur_offset, end] from ->bytes_may_use, but our extent
reservation will overlap part of this.

Fix this problem by adding ins.offset (our extent allocation size) to
cur_offset so we remove the actual remaining part from ->bytes_may_use.

I validated this fix using my inject-error.py script

python inject-error.py -o should_fail_bio -t cache_save_setup -t \
__btrfs_prealloc_file_range \
-t insert_reserved_file_extent.constprop.0 \
-r "-5" ./run-fsstress.sh

where run-fsstress.sh simply mounts and runs fsstress on a disk.

CC: stable@vger.kernel.org # 4.4+
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
fs/btrfs/inode.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)

--- a/fs/btrfs/inode.c
+++ b/fs/btrfs/inode.c
@@ -10639,6 +10639,7 @@ static int __btrfs_prealloc_file_range(s
struct btrfs_root *root = BTRFS_I(inode)->root;
struct btrfs_key ins;
u64 cur_offset = start;
+ u64 clear_offset = start;
u64 i_size;
u64 cur_bytes;
u64 last_alloc = (u64)-1;
@@ -10673,6 +10674,15 @@ static int __btrfs_prealloc_file_range(s
btrfs_end_transaction(trans);
break;
}
+
+ /*
+ * We've reserved this space, and thus converted it from
+ * ->bytes_may_use to ->bytes_reserved. Any error that happens
+ * from here on out we will only need to clear our reservation
+ * for the remaining unreserved area, so advance our
+ * clear_offset by our extent size.
+ */
+ clear_offset += ins.offset;
btrfs_dec_block_group_reservations(fs_info, ins.objectid);

last_alloc = ins.offset;
@@ -10753,9 +10763,9 @@ next:
if (own_trans)
btrfs_end_transaction(trans);
}
- if (cur_offset < end)
- btrfs_free_reserved_data_space(inode, NULL, cur_offset,
- end - cur_offset + 1);
+ if (clear_offset < end)
+ btrfs_free_reserved_data_space(inode, NULL, clear_offset,
+ end - clear_offset + 1);
return ret;
}


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