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| author | Cen Zhang <zzzccc427@gmail.com> | 2026-04-01 10:21:53 +0800 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2026-05-26 17:30:28 +0200 |
| commit | 161599423d1739ca202e35ece2bb37323091e5f4 (patch) | |
| tree | 12f4e926408bfc6a3467977c17e8ea04543c83f9 /fs | |
| parent | e56190b0a01176ca0706dd93399070a3d47e95d5 (diff) | |
| download | linux-next-history-161599423d1739ca202e35ece2bb37323091e5f4.tar.gz | |
btrfs: annotate lockless read of defrag_bytes in should_nocow()
should_nocow() reads inode->defrag_bytes without holding inode->lock,
while btrfs_set_delalloc_extent() and btrfs_clear_delalloc_extent()
update it under that spinlock.
This is a data race. The read is a quick check used to decide whether
to fall back to COW for a NOCOW inode: if defrag_bytes is non-zero and
the range is tagged EXTENT_DEFRAG, we force COW so that defragmentation
can rewrite the extent. Reading a stale value is harmless because:
- A missed increment may skip COW once, but the defrag pass will
redo the extent later.
- A stale non-zero may force an unnecessary COW, which is a minor
efficiency loss, not a correctness issue.
On 64-bit platforms an aligned u64 load is naturally atomic so tearing
cannot happen. On 32-bit platforms u64 may tear, but we only test for
zero vs non-zero, so the heuristic stays correct regardless. Use
data_race() annotation.
Fixes: 47059d930f0e ("Btrfs: make defragment work with nodatacow option")
Signed-off-by: Cen Zhang <zzzccc427@gmail.com>
[ Use data_race() instead of READ_ONCXE() ]
Signed-off-by: David Sterba <dsterba@suse.com>
Diffstat (limited to 'fs')
| -rw-r--r-- | fs/btrfs/inode.c | 2 |
1 files changed, 1 insertions, 1 deletions
diff --git a/fs/btrfs/inode.c b/fs/btrfs/inode.c index 9ce6200854672..61b5594c4206f 100644 --- a/fs/btrfs/inode.c +++ b/fs/btrfs/inode.c @@ -2293,7 +2293,7 @@ error: static bool should_nocow(struct btrfs_inode *inode, u64 start, u64 end) { if (inode->flags & (BTRFS_INODE_NODATACOW | BTRFS_INODE_PREALLOC)) { - if (inode->defrag_bytes && + if (data_race(inode->defrag_bytes) && btrfs_test_range_bit_exists(&inode->io_tree, start, end, EXTENT_DEFRAG)) return false; return true; |