diff options
| author | Filipe Manana <fdmanana@suse.com> | 2025-09-08 12:51:11 +0100 |
|---|---|---|
| committer | David Sterba <dsterba@suse.com> | 2025-09-15 05:25:43 +0200 |
| commit | 80eb65ccf6f72dc37b972583fe71cd8a50ff7e51 (patch) | |
| tree | a11e23151f9939a13f2f3bee9d13ebbdd7da8aba | |
| parent | 8679d2687c351824d08cf1f0e86f3b65f22a00fe (diff) | |
btrfs: annotate block group access with data_race() when sorting for reclaim
When sorting the block group list for reclaim we are using a block group's
used bytes counter without taking the block group's spinlock, so we can
race with a concurrent task updating it (at btrfs_update_block_group()),
which makes tools like KCSAN unhappy and report a race.
Since the sorting is not strictly needed from a functional perspective
and such races should rarely cause any ordering changes (only load/store
tearing could cause them), not to mention that after the sorting the
ordering may no longer be accurate due to concurrent allocations and
deallocations of extents in a block group, annotate the accesses to the
used counter with data_race() to silence KCSAN and similar tools.
Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Signed-off-by: Filipe Manana <fdmanana@suse.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>
| -rw-r--r-- | fs/btrfs/block-group.c | 9 |
1 files changed, 8 insertions, 1 deletions
diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index 9bf282d2453c..499a9edf0ca3 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -1795,7 +1795,14 @@ static int reclaim_bgs_cmp(void *unused, const struct list_head *a, bg1 = list_entry(a, struct btrfs_block_group, bg_list); bg2 = list_entry(b, struct btrfs_block_group, bg_list); - return bg1->used > bg2->used; + /* + * Some other task may be updating the ->used field concurrently, but it + * is not serious if we get a stale value or load/store tearing issues, + * as sorting the list of block groups to reclaim is not critical and an + * occasional imperfect order is ok. So silence KCSAN and avoid the + * overhead of locking or any other synchronization. + */ + return data_race(bg1->used > bg2->used); } static inline bool btrfs_should_reclaim(const struct btrfs_fs_info *fs_info) |