This is a note to let you know that I've just added the patch titled
btrfs: fix data race at btrfs_use_block_rsv() when accessing block reserve
to the 6.1-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
btrfs-fix-data-race-at-btrfs_use_block_rsv-when-acce.patch
and it can be found in the queue-6.1 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 91ab2a0aa6c75c52784e1d58aa3a712fa5bc48df
Author: Filipe Manana <fdmanana@xxxxxxxx>
Date: Mon Feb 19 20:10:07 2024 +0000
btrfs: fix data race at btrfs_use_block_rsv() when accessing block reserve
[ Upstream commit c7bb26b847e5b97814f522686068c5628e2b3646 ]
At btrfs_use_block_rsv() we read the size of a block reserve without
locking its spinlock, which makes KCSAN complain because the size of a
block reserve is always updated while holding its spinlock. The report
from KCSAN is the following:
[653.313148] BUG: KCSAN: data-race in btrfs_update_delayed_refs_rsv [btrfs] / btrfs_use_block_rsv [btrfs]
[653.314755] read to 0x000000017f5871b8 of 8 bytes by task 7519 on cpu 0:
[653.314779] btrfs_use_block_rsv+0xe4/0x2f8 [btrfs]
[653.315606] btrfs_alloc_tree_block+0xdc/0x998 [btrfs]
[653.316421] btrfs_force_cow_block+0x220/0xe38 [btrfs]
[653.317242] btrfs_cow_block+0x1ac/0x568 [btrfs]
[653.318060] btrfs_search_slot+0xda2/0x19b8 [btrfs]
[653.318879] btrfs_del_csums+0x1dc/0x798 [btrfs]
[653.319702] __btrfs_free_extent.isra.0+0xc24/0x2028 [btrfs]
[653.320538] __btrfs_run_delayed_refs+0xd3c/0x2390 [btrfs]
[653.321340] btrfs_run_delayed_refs+0xae/0x290 [btrfs]
[653.322140] flush_space+0x5e4/0x718 [btrfs]
[653.322958] btrfs_preempt_reclaim_metadata_space+0x102/0x2f8 [btrfs]
[653.323781] process_one_work+0x3b6/0x838
[653.323800] worker_thread+0x75e/0xb10
[653.323817] kthread+0x21a/0x230
[653.323836] __ret_from_fork+0x6c/0xb8
[653.323855] ret_from_fork+0xa/0x30
[653.323887] write to 0x000000017f5871b8 of 8 bytes by task 576 on cpu 3:
[653.323906] btrfs_update_delayed_refs_rsv+0x1a4/0x250 [btrfs]
[653.324699] btrfs_add_delayed_data_ref+0x468/0x6d8 [btrfs]
[653.325494] btrfs_free_extent+0x76/0x120 [btrfs]
[653.326280] __btrfs_mod_ref+0x6a8/0x6b8 [btrfs]
[653.327064] btrfs_dec_ref+0x50/0x70 [btrfs]
[653.327849] walk_up_proc+0x236/0xa50 [btrfs]
[653.328633] walk_up_tree+0x21c/0x448 [btrfs]
[653.329418] btrfs_drop_snapshot+0x802/0x1328 [btrfs]
[653.330205] btrfs_clean_one_deleted_snapshot+0x184/0x238 [btrfs]
[653.330995] cleaner_kthread+0x2b0/0x2f0 [btrfs]
[653.331781] kthread+0x21a/0x230
[653.331800] __ret_from_fork+0x6c/0xb8
[653.331818] ret_from_fork+0xa/0x30
So add a helper to get the size of a block reserve while holding the lock.
Reading the field while holding the lock instead of using the data_race()
annotation is used in order to prevent load tearing.
Signed-off-by: Filipe Manana <fdmanana@xxxxxxxx>
Reviewed-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: David Sterba <dsterba@xxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/fs/btrfs/block-rsv.c b/fs/btrfs/block-rsv.c
index 507b44d18572d..4cbf386166209 100644
--- a/fs/btrfs/block-rsv.c
+++ b/fs/btrfs/block-rsv.c
@@ -512,7 +512,7 @@ struct btrfs_block_rsv *btrfs_use_block_rsv(struct btrfs_trans_handle *trans,
block_rsv = get_block_rsv(trans, root);
- if (unlikely(block_rsv->size == 0))
+ if (unlikely(btrfs_block_rsv_size(block_rsv) == 0))
goto try_reserve;
again:
ret = btrfs_block_rsv_use_bytes(block_rsv, blocksize);
diff --git a/fs/btrfs/block-rsv.h b/fs/btrfs/block-rsv.h
index cda79d3e0c263..df87c4949d065 100644
--- a/fs/btrfs/block-rsv.h
+++ b/fs/btrfs/block-rsv.h
@@ -117,4 +117,20 @@ static inline u64 btrfs_block_rsv_reserved(struct btrfs_block_rsv *rsv)
return ret;
}
+/*
+ * Get the size of a block reserve in a context where getting a stale value is
+ * acceptable, instead of accessing it directly and trigger data race warning
+ * from KCSAN.
+ */
+static inline u64 btrfs_block_rsv_size(struct btrfs_block_rsv *rsv)
+{
+ u64 ret;
+
+ spin_lock(&rsv->lock);
+ ret = rsv->size;
+ spin_unlock(&rsv->lock);
+
+ return ret;
+}
+
#endif /* BTRFS_BLOCK_RSV_H */
