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

Chao Yu
2025-11-26T03:58:35Z

On 11/26/25 11:37, Chaitanya Kulkarni wrote:
> 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.

Yes, I think you're right, thanks for the explanation.

So it's fine to leave this cleanup patch as it is, and let's fix this bug in
a separated patch.

Thanks,

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