@@ -286,7 +286,7 @@ 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)
@@ -92,4 +92,13 @@ 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 */
@@ -594,7 +594,7 @@ 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;
}
@@ -619,7 +619,7 @@ 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
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@mail.gmail.com/ Link: https://lore.kernel.org/linux-btrfs/YvHU/vsXd7uz5V6j@hungrycats.org Reported-by: Zygo Blaxell <ce3g8jdj@umail.furryterror.org> Signed-off-by: David Sterba <dsterba@suse.com> --- fs/btrfs/block-rsv.c | 2 +- fs/btrfs/block-rsv.h | 9 +++++++++ fs/btrfs/transaction.c | 4 ++-- 3 files changed, 12 insertions(+), 3 deletions(-)