f2fs: fix to avoid running out of free segments

If checkpoint is disabled, GC can not reclaim any segments, we need
to detect such condition and bail out from fallocate() of a pinfile,
rather than letting allocator running out of free segment, which may
cause f2fs to be shutdown.

reproducer:
mkfs.f2fs -f /dev/vda 16777216
mount -o checkpoint=disable:10% /dev/vda /mnt/f2fs
for ((i=0;i<4096;i++)) do { dd if=/dev/zero of=/mnt/f2fs/$i bs=1M count=1; } done
sync
for ((i=0;i<4096;i+=2)) do { rm /mnt/f2fs/$i; } done
sync
touch /mnt/f2fs/pinfile
f2fs_io pinfile set /mnt/f2fs/pinfile
f2fs_io fallocate 0 0 4201644032 /mnt/f2fs/pinfile

cat /sys/kernel/debug/f2fs/status
output:
  - Free: 0 (0)

Fixes: f5a53ed ("f2fs: support aligned pinned file")
Signed-off-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

Author: chaseyu

fs/f2fs/file.c

@@ -1838,6 +1838,18 @@ static int f2fs_expand_inode_data(struct inode *inode, loff_t offset,
 next_alloc:
 		f2fs_down_write(&sbi->pin_sem);
 
+		if (unlikely(is_sbi_flag_set(sbi, SBI_CP_DISABLED))) {
+			if (has_not_enough_free_secs(sbi, 0, 0)) {
+				f2fs_up_write(&sbi->pin_sem);
+				err = -ENOSPC;
+				f2fs_warn_ratelimited(sbi,
+					"ino:%lu, start:%lu, end:%lu, need to trigger GC to "
+					"reclaim enough free segment when checkpoint is enabled",
+					inode->i_ino, pg_start, pg_end);
+				goto out_err;
+			}
+		}
+
 		if (has_not_enough_free_secs(sbi, 0, f2fs_sb_has_blkzoned(sbi) ?
 			ZONED_PIN_SEC_REQUIRED_COUNT :
 			GET_SEC_FROM_SEG(sbi, overprovision_segments(sbi)))) {