Re: [PATCH] block: Fix __blkdev_direct_IO()

[Jens Axboe <axboe@kernel.dk>]

On 8/9/19 6:01 AM, Damien Le Moal wrote:
> On 2019/08/07 4:53, Jens Axboe wrote:
>>> Hi Damien,
>>>
>>> Had you verified this patch with blktests and KASAN enabled? I think the
>>> above patch introduced the following KASAN complaint:
>>
>> I posted this in another thread, can you try?
>>
>>
>> diff --git a/fs/block_dev.c b/fs/block_dev.c
>> index a6f7c892cb4a..131e2e0582a6 100644
>> --- a/fs/block_dev.c
>> +++ b/fs/block_dev.c
>> @@ -349,7 +349,7 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>   	loff_t pos = iocb->ki_pos;
>>   	blk_qc_t qc = BLK_QC_T_NONE;
>>   	gfp_t gfp;
>> -	ssize_t ret;
>> +	int ret;
>>   
>>   	if ((pos | iov_iter_alignment(iter)) &
>>   	    (bdev_logical_block_size(bdev) - 1))
>> @@ -386,8 +386,6 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>   
>>   	ret = 0;
>>   	for (;;) {
>> -		int err;
>> -
>>   		bio_set_dev(bio, bdev);
>>   		bio->bi_iter.bi_sector = pos >> 9;
>>   		bio->bi_write_hint = iocb->ki_hint;
>> @@ -395,10 +393,8 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>   		bio->bi_end_io = blkdev_bio_end_io;
>>   		bio->bi_ioprio = iocb->ki_ioprio;
>>   
>> -		err = bio_iov_iter_get_pages(bio, iter);
>> -		if (unlikely(err)) {
>> -			if (!ret)
>> -				ret = err;
>> +		ret = bio_iov_iter_get_pages(bio, iter);
>> +		if (unlikely(ret)) {
>>   			bio->bi_status = BLK_STS_IOERR;
>>   			bio_endio(bio);
>>   			break;
>> @@ -421,7 +417,6 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>   		if (nowait)
>>   			bio->bi_opf |= (REQ_NOWAIT | REQ_NOWAIT_INLINE);
>>   
>> -		dio->size += bio->bi_iter.bi_size;
>>   		pos += bio->bi_iter.bi_size;
>>   
>>   		nr_pages = iov_iter_npages(iter, BIO_MAX_PAGES);
>> @@ -433,13 +428,13 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>   				polled = true;
>>   			}
>>   
>> +			dio->size += bio->bi_iter.bi_size;
>>   			qc = submit_bio(bio);
>>   			if (qc == BLK_QC_T_EAGAIN) {
>> -				if (!ret)
>> -					ret = -EAGAIN;
>> +				dio->size -= bio->bi_iter.bi_size;
>> +				ret = -EAGAIN;
>>   				goto error;
>>   			}
>> -			ret = dio->size;
>>   
>>   			if (polled)
>>   				WRITE_ONCE(iocb->ki_cookie, qc);
>> @@ -460,18 +455,17 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>   			atomic_inc(&dio->ref);
>>   		}
>>   
>> +		dio->size += bio->bi_iter.bi_size;
>>   		qc = submit_bio(bio);
>>   		if (qc == BLK_QC_T_EAGAIN) {
>> -			if (!ret)
>> -				ret = -EAGAIN;
>> +			dio->size -= bio->bi_iter.bi_size;
>> +			ret = -EAGAIN;
>>   			goto error;
>>   		}
>> -		ret = dio->size;
>>   
>>   		bio = bio_alloc(gfp, nr_pages);
>>   		if (!bio) {
>> -			if (!ret)
>> -				ret = -EAGAIN;
>> +			ret = -EAGAIN;
>>   			goto error;
>>   		}
>>   	}
>> @@ -496,6 +490,8 @@ __blkdev_direct_IO(struct kiocb *iocb, struct iov_iter *iter, int nr_pages)
>>   out:
>>   	if (!ret)
>>   		ret = blk_status_to_errno(dio->bio.bi_status);
>> +	if (likely(!ret))
>> +		ret = dio->size;
>>   
>>   	bio_put(&dio->bio);
>>   	return ret;
>>
> 
> Jens,
> 
> I tested a slightly modified version of your patch. I think it is 100%
> equivalent, but a little cleaner in my opinion.

[snip]

I already queued up the other one days ago, don't think there's much
difference between them. In any case, I've read your full email and I'll
take a look at the NOWAIT + sync case. I'm currently out though, so it
won't be until Monday. Because of that, I'll ship what I have today as
it fixes the most common case, then go over the sync+nowait on Monday to
see what's up there.

-- 
Jens Axboe