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	id 5975668BFE; Wed,  8 Jul 2026 18:24:35 +0200 (CEST)
Date: Wed, 8 Jul 2026 18:24:35 +0200
From: Christoph Hellwig <hch@lst.de>
To: Joseph Qi <joseph.qi@linux.alibaba.com>
Cc: Pankaj Gupta <pankaj.gupta.linux@gmail.com>,
	virtualization@lists.linux.dev, linux-kernel@vger.kernel.org,
	Christoph Hellwig <hch@lst.de>,
	Baokun Li <libaokun@linux.alibaba.com>
Subject: Re: [PATCH] virtio-pmem: use GFP_NOIO for flush bio allocation
Message-ID: <20260708162435.GB2502@lst.de>
References: <20260708124238.2817165-1-joseph.qi@linux.alibaba.com>
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User-Agent: Mutt/1.5.17 (2007-11-01)

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.