f2fs: avoid swapon failure by giving a warning first

The final solution can be migrating blocks to form a section-aligned file
internally. Meanwhile, let's ask users to do that when preparing the swap
file initially like:
1) create()
2) ioctl(F2FS_IOC_SET_PIN_FILE)
3) fallocate()
Reported-by: kernel test robot <oliver.sang@intel.com>
Fixes: 36e4d958 ("f2fs: check if swapfile is section-alligned")
Reviewed-by: Chao Yu <yuchao0@huawei.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/data.c

@@ -3801,6 +3801,7 @@ static int f2fs_is_file_aligned(struct inode *inode)
 	block_t pblock;
 	unsigned long nr_pblocks;
 	unsigned int blocks_per_sec = BLKS_PER_SEC(sbi);
+	unsigned int not_aligned = 0;
 	int ret = 0;
 
 	cur_lblock = 0;
@@ -3833,13 +3834,20 @@ static int f2fs_is_file_aligned(struct inode *inode)
 
 		if ((pblock - main_blkaddr) & (blocks_per_sec - 1) ||
 			nr_pblocks & (blocks_per_sec - 1)) {
+			if (f2fs_is_pinned_file(inode)) {
 				f2fs_err(sbi, "Swapfile does not align to section");
 				ret = -EINVAL;
 				goto out;
 			}
+			not_aligned++;
+		}
 
 		cur_lblock += nr_pblocks;
 	}
+	if (not_aligned)
+		f2fs_warn(sbi, "Swapfile (%u) is not align to section: \n"
+			"\t1) creat(), 2) ioctl(F2FS_IOC_SET_PIN_FILE), 3) fallocate()",
+			not_aligned);
 out:
 	return ret;
 }
@@ -3858,6 +3866,7 @@ static int check_swap_activate_fast(struct swap_info_struct *sis,
 	int nr_extents = 0;
 	unsigned long nr_pblocks;
 	unsigned int blocks_per_sec = BLKS_PER_SEC(sbi);
+	unsigned int not_aligned = 0;
 	int ret = 0;
 
 	/*
@@ -3896,10 +3905,13 @@ static int check_swap_activate_fast(struct swap_info_struct *sis,
 
 		if ((pblock - SM_I(sbi)->main_blkaddr) & (blocks_per_sec - 1) ||
 				nr_pblocks & (blocks_per_sec - 1)) {
+			if (f2fs_is_pinned_file(inode)) {
 				f2fs_err(sbi, "Swapfile does not align to section");
 				ret = -EINVAL;
 				goto out;
 			}
+			not_aligned++;
+		}
 
 		if (cur_lblock + nr_pblocks >= sis->max)
 			nr_pblocks = sis->max - cur_lblock;
@@ -3927,6 +3939,11 @@ static int check_swap_activate_fast(struct swap_info_struct *sis,
 	sis->max = cur_lblock;
 	sis->pages = cur_lblock - 1;
 	sis->highest_bit = cur_lblock - 1;
+
+	if (not_aligned)
+		f2fs_warn(sbi, "Swapfile (%u) is not align to section: \n"
+			"\t1) creat(), 2) ioctl(F2FS_IOC_SET_PIN_FILE), 3) fallocate()",
+			not_aligned);
 out:
 	return ret;
 }