6.12-stable review patch. If anyone has any objections, please let me know.
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From: Filipe Manana fdmanana@suse.com
[ Upstream commit 1283b8c125a83bf7a7dbe90c33d3472b6d7bf612 ]
At btrfs_reclaim_bgs_work(), we are grabbing a block group's zone unusable bytes while not under the protection of the block group's spinlock, so this can trigger race reports from KCSAN (or similar tools) since that field is typically updated while holding the lock, such as at __btrfs_add_free_space_zoned() for example.
Fix this by grabbing the zone unusable bytes while we are still in the critical section holding the block group's spinlock, which is right above where we are currently grabbing it.
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 Signed-off-by: Sasha Levin sashal@kernel.org --- fs/btrfs/block-group.c | 18 +++++++++++------- 1 file changed, 11 insertions(+), 7 deletions(-)
diff --git a/fs/btrfs/block-group.c b/fs/btrfs/block-group.c index 4423d8b716a58..aa8656c8b7e7e 100644 --- a/fs/btrfs/block-group.c +++ b/fs/btrfs/block-group.c @@ -1891,6 +1891,17 @@ void btrfs_reclaim_bgs_work(struct work_struct *work) up_write(&space_info->groups_sem); goto next; } + + /* + * Cache the zone_unusable value before turning the block group + * to read only. As soon as the block group is read only it's + * zone_unusable value gets moved to the block group's read-only + * bytes and isn't available for calculations anymore. We also + * cache it before unlocking the block group, to prevent races + * (reports from KCSAN and such tools) with tasks updating it. + */ + zone_unusable = bg->zone_unusable; + spin_unlock(&bg->lock); spin_unlock(&space_info->lock);
@@ -1907,13 +1918,6 @@ void btrfs_reclaim_bgs_work(struct work_struct *work) goto next; }
- /* - * Cache the zone_unusable value before turning the block group - * to read only. As soon as the blog group is read only it's - * zone_unusable value gets moved to the block group's read-only - * bytes and isn't available for calculations anymore. - */ - zone_unusable = bg->zone_unusable; ret = inc_block_group_ro(bg, 0); up_write(&space_info->groups_sem); if (ret < 0)