f2fs: Keep alloc_valid_block_count in sync

If we attempt to request more blocks than we have room for, we try to
instead request as much as we can, however, alloc_valid_block_count
is not decremented to match the new value, allowing it to drift higher
until the next checkpoint. This always decrements it when the requested
amount cannot be fulfilled.
Signed-off-by: Daniel Rosenberg <drosen@google.com>
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/f2fs.h

@@ -1686,18 +1686,20 @@ static inline int inc_valid_block_count(struct f2fs_sb_info *sbi,
 		sbi->total_valid_block_count -= diff;
 		if (!*count) {
 			spin_unlock(&sbi->stat_lock);
-			percpu_counter_sub(&sbi->alloc_valid_block_count, diff);
 			goto enospc;
 		}
 	}
 	spin_unlock(&sbi->stat_lock);
 
-	if (unlikely(release))
+	if (unlikely(release)) {
+		percpu_counter_sub(&sbi->alloc_valid_block_count, release);
 		dquot_release_reservation_block(inode, release);
+	}
 	f2fs_i_blocks_write(inode, *count, true, true);
 	return 0;
 
 enospc:
+	percpu_counter_sub(&sbi->alloc_valid_block_count, release);
 	dquot_release_reservation_block(inode, release);
 	return -ENOSPC;
 }