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

[Chaitanya Kulkarni <chaitanyak@nvidia.com>]

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