Re: [PATCH] virtio-pmem: use GFP_NOIO for flush bio allocation

[Joseph Qi]

On 7/9/26 12:24 AM, Christoph Hellwig wrote:
> On Wed, Jul 08, 2026 at 08:42:38PM +0800, Joseph Qi wrote:
>> diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c
>> index 4176046627beb..081370aac6317 100644
>> --- a/drivers/nvdimm/nd_virtio.c
>> +++ b/drivers/nvdimm/nd_virtio.c
>> @@ -117,7 +117,7 @@ int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
>>  	if (bio && bio->bi_iter.bi_sector != -1) {
>>  		struct bio *child = bio_alloc(bio->bi_bdev, 0,
>>  					      REQ_OP_WRITE | REQ_PREFLUSH,
>> -					      GFP_ATOMIC);
>> +					      GFP_NOIO);
>>  
>>  		if (!child)
>>  			return -ENOMEM;
> 
> This NULL  check can go away now, and probaby should to avoid confusion.
> 
> Also bio_alloc allocates from fs_bio_set, so if the incoming bio
> is from that, we can still deadlock.  We'll need a separate bio_set
> for this to be deadlock free.  disk->bio_split isn't otherwise
> used for the drivers/nvdimm/ driverss, so you might be able to
> repurpose that if you want to be creative.

Thanks for pointing this out.

Seems it is more proper to use a driver-private bio_set instead of
repurposing bd_disk->bio_split, like raid5-ppl flush_bs.

Pankaj, what's your opinion?

Thanks,
Joseph