[PATCH v3 1/3] ext4: fix incorrect calculate 'reserved' in '__es_remove_extent' when enable bigalloc feature

[Ye Bin <yebin@huaweicloud.com>]

From: Ye Bin <yebin10@huawei.com>

Syzbot report issue as follows:
EXT4-fs error (device loop0): ext4_validate_block_bitmap:398: comm rep: bg 0: block 5: invalid block bitmap
EXT4-fs (loop0): Delayed block allocation failed for inode 18 at logical offset 0 with max blocks 32 with error 28
EXT4-fs (loop0): This should not happen!! Data will be lost

EXT4-fs (loop0): Total free blocks count 0
EXT4-fs (loop0): Free/Dirty block details
EXT4-fs (loop0): free_blocks=0
EXT4-fs (loop0): dirty_blocks=32
EXT4-fs (loop0): Block reservation details
EXT4-fs (loop0): i_reserved_data_blocks=2
EXT4-fs (loop0): Inode 18 (00000000845cd634): i_reserved_data_blocks (1) not cleared!

Above issue happens as follows:
Assume:
sbi->s_cluster_ratio = 16
Step1: Insert delay block [0, 31] -> ei->i_reserved_data_blocks=2
Step2:
ext4_writepages
  mpage_map_and_submit_extent -> return failed
  mpage_release_unused_pages -> to release [0, 30]
    ext4_es_remove_extent -> remove lblk=0 end=30
      __es_remove_extent -> len1=0 len2=31-30=1
 __es_remove_extent:
 ...
 if (len2 > 0) {
  ...
	  if (len1 > 0) {
		  ...
	  } else {
		es->es_lblk = end + 1;
		es->es_len = len2;
		...
	  }
  	if (count_reserved)
		count_rsvd(inode, lblk, orig_es.es_len - len1 - len2, &orig_es, &rc);
	goto out; -> will return but didn't calculate 'reserved'
 ...
Step3: ext4_destroy_inode -> trigger "i_reserved_data_blocks (1) not cleared!"

To solve above issue if 'len2>0' call 'get_rsvd()' before goto out.

Reported-by: syzbot+05a0f0ccab4a25626e38@syzkaller.appspotmail.com
Fixes: 8fcc3a580651 ("ext4: rework reserved cluster accounting when invalidating pages")
Signed-off-by: Ye Bin <yebin10@huawei.com>
---
 fs/ext4/extents_status.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/fs/ext4/extents_status.c b/fs/ext4/extents_status.c
index cd0a861853e3..7ada374ff27d 100644
--- a/fs/ext4/extents_status.c
+++ b/fs/ext4/extents_status.c
@@ -1371,7 +1371,7 @@ static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
 		if (count_reserved)
 			count_rsvd(inode, lblk, orig_es.es_len - len1 - len2,
 				   &orig_es, &rc);
-		goto out;
+		goto out_get_reserved;
 	}
 
 	if (len1 > 0) {
@@ -1413,6 +1413,7 @@ static int __es_remove_extent(struct inode *inode, ext4_lblk_t lblk,
 		}
 	}
 
+out_get_reserved:
 	if (count_reserved)
 		*reserved = get_rsvd(inode, end, es, &rc);
 out:
-- 
2.31.1