Re: [PATCH V3 5/6] f2fs: ignore discard return value

Chaitanya Kulkarni
2025-11-26T03:37:23Z

On 11/25/25 18:47, Chao Yu wrote:
> On 11/25/25 07:48, Chaitanya Kulkarni wrote:
>> __blkdev_issue_discard() always returns 0, making the error assignment
>> in __submit_discard_cmd() dead code.
>>
>> Initialize err to 0 and remove the error assignment from the
>> __blkdev_issue_discard() call to err. Move fault injection code into
>> already present if branch where err is set to -EIO.
>>
>> This preserves the fault injection behavior while removing dead error
>> handling.
>>
>> Reviewed-by: Martin K. Petersen <martin.petersen@oracle.com>
>> Reviewed-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
>> Reviewed-by: Christoph Hellwig <hch@lst.de>
>> Signed-off-by: Chaitanya Kulkarni <ckulkarnilinux@gmail.com>
>> ---
>> fs/f2fs/segment.c | 10 +++-------
>> 1 file changed, 3 insertions(+), 7 deletions(-)
>>
>> diff --git a/fs/f2fs/segment.c b/fs/f2fs/segment.c
>> index b45eace879d7..22b736ec9c51 100644
>> --- a/fs/f2fs/segment.c
>> +++ b/fs/f2fs/segment.c
>> @@ -1343,15 +1343,9 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>>
>> dc->di.len += len;
>>
>> + err = 0;
>> if (time_to_inject(sbi, FAULT_DISCARD)) {
>> err = -EIO;
>> - } else {
>> - err = __blkdev_issue_discard(bdev,
>> - SECTOR_FROM_BLOCK(start),
>> - SECTOR_FROM_BLOCK(len),
>> - GFP_NOFS, &bio);
>> - }
>> - if (err) {
>> spin_lock_irqsave(&dc->lock, flags);
>> if (dc->state == D_PARTIAL)
>> dc->state = D_SUBMIT;
>> @@ -1360,6 +1354,8 @@ static int __submit_discard_cmd(struct f2fs_sb_info *sbi,
>> break;
>> }
>>
>> + __blkdev_issue_discard(bdev, SECTOR_FROM_BLOCK(start),
>> + SECTOR_FROM_BLOCK(len), GFP_NOFS, &bio);
> Oh, wait, bio can be NULL? Then below f2fs_bug_on() will trigger panic or warning.
>
> Thanks,

That will happen without this patch also or not ?

Since __blkdev_issue_discard() is always returning 0 irrespective of bio
is null or not.

The following condition in original code will only execute when err is set to
-EIO and that will only happen when time_to_inject() -> true.
Original call to __blkdev_issue_discard() without this patch will always
return 0 even for bio == NULL after __blkdev_issue_discard().

This is what we are trying to fix so caller should not rely on
__blkdev_issue_discard() return value :-

354 if (err) {
1355 spin_lock_irqsave(&dc->lock, flags);
1356 if (dc->state == D_PARTIAL)
1357 dc->state = D_SUBMIT;
1358 spin_unlock_irqrestore(&dc->lock, flags);
1359
1360 break;
1361 }

which will lead f2fs_bug_on() for bio == NULL even without this patch.

This patch is not changing exiting behavior, correct me if I'm wrong.

>
>> f2fs_bug_on(sbi, !bio);
>>
>> /*

-ck