The functions btrfs_block_rsv_release() and
btrfs_update_delayed_refs_rsv() are concurrently executed at runtime in
the following call contexts:
Thread 1:
btrfs_file_write_iter()
btrfs_buffered_write()
btrfs_delalloc_release_extents()
btrfs_inode_rsv_release()
__btrfs_block_rsv_release()
Thread 2:
finish_ordered_fn()
btrfs_finish_ordered_io()
insert_reserved_file_extent()
__btrfs_drop_extents()
btrfs_free_extent()
btrfs_add_delayed_data_ref()
btrfs_update_delayed_refs_rsv()
In __btrfs_block_rsv_release():
else if (... && !delayed_rsv->full)
In btrfs_update_delayed_refs_rsv():
spin_lock(&delayed_rsv->lock);
delayed_rsv->size += num_bytes;
delayed_rsv->full = 0;
spin_unlock(&delayed_rsv->lock);
Thus a data race for delayed_rsv->full can occur.
This race was found and actually reproduced by our conccurency fuzzer.
To fix this race, the spinlock delayed_rsv->lock is used to
protect the access to delayed_rsv->full in btrfs_block_rsv_release().
Signed-off-by: Jia-Ju Bai <baijiaju1990@xxxxxxxxx>
---
fs/btrfs/block-rsv.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c
index 27efec8f7c5b..89c53a7137b4 100644
--- a/fs/btrfs/block-rsv.c
+++ b/fs/btrfs/block-rsv.c
@@ -277,6 +277,11 @@ u64 btrfs_block_rsv_release(struct btrfs_fs_info *fs_info,
struct btrfs_block_rsv *global_rsv = &fs_info->global_block_rsv;
struct btrfs_block_rsv *delayed_rsv = &fs_info->delayed_refs_rsv;
struct btrfs_block_rsv *target = NULL;
+ unsigned short full = 0;
+
+ spin_lock(&delayed_rsv->lock);
+ full = delayed_rsv->full;
+ spin_unlock(&delayed_rsv->lock);
/*
* If we are the delayed_rsv then push to the global rsv, otherwise dump
@@ -284,7 +289,7 @@ u64 btrfs_block_rsv_release(struct btrfs_fs_info *fs_info,
*/
if (block_rsv == delayed_rsv)
target = global_rsv;
- else if (block_rsv != global_rsv && !delayed_rsv->full)
+ else if (block_rsv != global_rsv && !full)
target = delayed_rsv;
if (target && block_rsv->space_info != target->space_info)
--
2.17.1
