f2fs: stop checkpoint when get a out-of-bounds segment

There is low probability that an out-of-bounds segment will be got
on a small-capacity device. In order to prevent subsequent write requests
allocating block address from this invalid segment, which may cause
unexpected issue, stop checkpoint should be performed.

Also introduce a new stop cp reason: STOP_CP_REASON_NO_SEGMENT.

Note, f2fs_stop_checkpoint(, false) is complex and it may sleep, so we should
move it outside segmap_lock spinlock coverage in get_new_segment().
Signed-off-by: Zhiguo Niu <zhiguo.niu@unisoc.com>
Reviewed-by: Chao Yu <chao@kernel.org>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/segment.c

@@ -2649,6 +2649,7 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
 	unsigned int old_zoneno = GET_ZONE_FROM_SEG(sbi, *newseg);
 	bool init = true;
 	int i;
+	int ret = 0;
 
 	spin_lock(&free_i->segmap_lock);
 
@@ -2673,7 +2674,10 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
 	if (secno >= MAIN_SECS(sbi)) {
 		secno = find_first_zero_bit(free_i->free_secmap,
 							MAIN_SECS(sbi));
-		f2fs_bug_on(sbi, secno >= MAIN_SECS(sbi));
+		if (secno >= MAIN_SECS(sbi)) {
+			ret = -ENOSPC;
+			goto out_unlock;
+		}
 	}
 	segno = GET_SEG_FROM_SEC(sbi, secno);
 	zoneno = GET_ZONE_FROM_SEC(sbi, secno);
@@ -2703,7 +2707,13 @@ static void get_new_segment(struct f2fs_sb_info *sbi,
 	f2fs_bug_on(sbi, test_bit(segno, free_i->free_segmap));
 	__set_inuse(sbi, segno);
 	*newseg = segno;
+out_unlock:
 	spin_unlock(&free_i->segmap_lock);
+
+	if (ret) {
+		f2fs_stop_checkpoint(sbi, false, STOP_CP_REASON_NO_SEGMENT);
+		f2fs_bug_on(sbi, 1);
+	}
 }
 
 static void reset_curseg(struct f2fs_sb_info *sbi, int type, int modified)

include/linux/f2fs_fs.h

@@ -75,6 +75,7 @@ enum stop_cp_reason {
 	STOP_CP_REASON_CORRUPTED_SUMMARY,
 	STOP_CP_REASON_UPDATE_INODE,
 	STOP_CP_REASON_FLUSH_FAIL,
+	STOP_CP_REASON_NO_SEGMENT,
 	STOP_CP_REASON_MAX,
 };