This is a note to let you know that I've just added the patch titled
btrfs: add KCSAN annotations for unlocked access to block_rsv->full
to the 5.15-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-add-kcsan-annotations-for-unlocked-access-to-b.patch
and it can be found in the queue-5.15 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit 4524d3949d0bf4877bf901de76095f3818c3f1dc
Author: David Sterba <dsterba@xxxxxxxx>
Date: Mon Sep 5 18:32:23 2022 +0200
btrfs: add KCSAN annotations for unlocked access to block_rsv->full
[ Upstream commit 748f553c3c4c4f175c6c834358632aff802d72cf ]
KCSAN reports that there's unlocked access mixed with locked access,
which is technically correct but is not a bug. To avoid false alerts at
least from KCSAN, add annotation and use a wrapper whenever ->full is
accessed for read outside of lock.
It is used as a fast check and only advisory. In the worst case the
block reserve is found !full and becomes full in the meantime, but
properly handled.
Depending on the value of ->full, btrfs_block_rsv_release decides
where to return the reservation, and block_rsv_release_bytes handles a
NULL pointer for block_rsv and if it's not NULL then it double checks
the full status under a lock.
Link: https://lore.kernel.org/linux-btrfs/CAAwBoOJDjei5Hnem155N_cJwiEkVwJYvgN-tQrwWbZQGhFU=cA@xxxxxxxxxxxxxx/
Link: https://lore.kernel.org/linux-btrfs/YvHU/vsXd7uz5V6j@xxxxxxxxxxxxxx
Reported-by: Zygo Blaxell <ce3g8jdj@xxxxxxxxxxxxxxxxxxxxx>
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 04a6226e0388..3e0eb69b6d4e 100644
--- a/fs/btrfs/block-rsv.c
+++ b/fs/btrfs/block-rsv.c
@@ -285,7 +285,7 @@ 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 && !btrfs_block_rsv_full(delayed_rsv))
target = delayed_rsv;
if (target && block_rsv->space_info != target->space_info)
diff --git a/fs/btrfs/block-rsv.h b/fs/btrfs/block-rsv.h
index 0b6ae5302837..f0431547acf2 100644
--- a/fs/btrfs/block-rsv.h
+++ b/fs/btrfs/block-rsv.h
@@ -90,4 +90,13 @@ static inline void btrfs_unuse_block_rsv(struct btrfs_fs_info *fs_info,
btrfs_block_rsv_release(fs_info, block_rsv, 0, NULL);
}
+/*
+ * Fast path to check if the reserve is full, may be carefully used outside of
+ * locks.
+ */
+static inline bool btrfs_block_rsv_full(const struct btrfs_block_rsv *rsv)
+{
+ return data_race(rsv->full);
+}
+
#endif /* BTRFS_BLOCK_RSV_H */
diff --git a/fs/btrfs/transaction.c b/fs/btrfs/transaction.c
index 642cd2b55fa0..6b6a1a277f01 100644
--- a/fs/btrfs/transaction.c
+++ b/fs/btrfs/transaction.c
@@ -619,7 +619,7 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
*/
num_bytes = btrfs_calc_insert_metadata_size(fs_info, num_items);
if (flush == BTRFS_RESERVE_FLUSH_ALL &&
- delayed_refs_rsv->full == 0) {
+ btrfs_block_rsv_full(delayed_refs_rsv) == 0) {
delayed_refs_bytes = num_bytes;
num_bytes <<= 1;
}
@@ -644,7 +644,7 @@ start_transaction(struct btrfs_root *root, unsigned int num_items,
if (rsv->space_info->force_alloc)
do_chunk_alloc = true;
} else if (num_items == 0 && flush == BTRFS_RESERVE_FLUSH_ALL &&
- !delayed_refs_rsv->full) {
+ !btrfs_block_rsv_full(delayed_refs_rsv)) {
/*
* Some people call with btrfs_start_transaction(root, 0)
* because they can be throttled, but have some other mechanism
