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Date:   Tue, 14 May 2019 05:47:22 -0400 (EDT)
From:   Pankaj Gupta <pagupta@...hat.com>
To:     David Hildenbrand <david@...hat.com>
Cc:     linux-nvdimm@...ts.01.org, linux-kernel@...r.kernel.org,
        virtualization@...ts.linux-foundation.org, kvm@...r.kernel.org,
        linux-fsdevel@...r.kernel.org, linux-acpi@...r.kernel.org,
        qemu-devel@...gnu.org, linux-ext4@...r.kernel.org,
        linux-xfs@...r.kernel.org,
        dan j williams <dan.j.williams@...el.com>,
        zwisler@...nel.org, vishal l verma <vishal.l.verma@...el.com>,
        dave jiang <dave.jiang@...el.com>, mst@...hat.com,
        jasowang@...hat.com, willy@...radead.org, rjw@...ysocki.net,
        hch@...radead.org, lenb@...nel.org, jack@...e.cz, tytso@....edu,
        adilger kernel <adilger.kernel@...ger.ca>,
        darrick wong <darrick.wong@...cle.com>, lcapitulino@...hat.com,
        kwolf@...hat.com, imammedo@...hat.com, jmoyer@...hat.com,
        nilal@...hat.com, riel@...riel.com, stefanha@...hat.com,
        aarcange@...hat.com, david@...morbit.com, cohuck@...hat.com,
        xiaoguangrong eric <xiaoguangrong.eric@...il.com>,
        pbonzini@...hat.com, kilobyte@...band.pl,
        yuval shaia <yuval.shaia@...cle.com>, jstaron@...gle.com
Subject: Re: [PATCH v8 2/6] virtio-pmem: Add virtio pmem driver


> 
> >>
> >>> +	}
> >>> +
> >>> +	/* When host has read buffer, this completes via host_ack */
> >>
> >> "A host repsonse results in "host_ack" getting called" ... ?
> >>
> >>> +	wait_event(req->host_acked, req->done);
> >>> +	err = req->ret;
> >>> +ret:
> >>> +	kfree(req);
> >>> +	return err;
> >>> +};
> >>> +
> >>> +/* The asynchronous flush callback function */
> >>> +int async_pmem_flush(struct nd_region *nd_region, struct bio *bio)
> >>> +{
> >>> +	int rc = 0;
> >>> +
> >>> +	/* Create child bio for asynchronous flush and chain with
> >>> +	 * parent bio. Otherwise directly call nd_region flush.
> >>> +	 */
> >>> +	if (bio && bio->bi_iter.bi_sector != -1) {
> >>> +		struct bio *child = bio_alloc(GFP_ATOMIC, 0);
> >>> +
> >>> +		if (!child)
> >>> +			return -ENOMEM;
> >>> +		bio_copy_dev(child, bio);
> >>> +		child->bi_opf = REQ_PREFLUSH;
> >>> +		child->bi_iter.bi_sector = -1;
> >>> +		bio_chain(child, bio);
> >>> +		submit_bio(child);
> >>
> >> return 0;
> >>
> >> Then, drop the "else" case and "int rc" and do directly
> >>
> >> if (virtio_pmem_flush(nd_region))
> >> 	return -EIO;
> > 
> > and another 'return 0' here :)
> > 
> > I don't like return from multiple places instead I prefer
> > single exit point from function.
> 
> Makes this function more complicated than necessary. I agree when there
> are locks involved.

o.k. I will change as you suggest :)

> 
> >  
> >>
> >>> +
> >>> +	return 0;
> >>> +};
> >>> +
> >>> +static int virtio_pmem_probe(struct virtio_device *vdev)
> >>> +{
> >>> +	int err = 0;
> >>> +	struct resource res;
> >>> +	struct virtio_pmem *vpmem;
> >>> +	struct nd_region_desc ndr_desc = {};
> >>> +	int nid = dev_to_node(&vdev->dev);
> >>> +	struct nd_region *nd_region;
> >>
> >> Nit: use reverse Christmas tree layout :)
> > 
> > Done.
> > 
> >>
> >>> +
> >>> +	if (!vdev->config->get) {
> >>> +		dev_err(&vdev->dev, "%s failure: config access disabled\n",
> >>> +			__func__);
> >>> +		return -EINVAL;
> >>> +	}
> >>> +
> >>> +	vpmem = devm_kzalloc(&vdev->dev, sizeof(*vpmem), GFP_KERNEL);
> >>> +	if (!vpmem) {
> >>> +		err = -ENOMEM;
> >>> +		goto out_err;
> >>> +	}
> >>> +
> >>> +	vpmem->vdev = vdev;
> >>> +	vdev->priv = vpmem;
> >>> +	err = init_vq(vpmem);
> >>> +	if (err)
> >>> +		goto out_err;
> >>> +
> >>> +	virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> >>> +			start, &vpmem->start);
> >>> +	virtio_cread(vpmem->vdev, struct virtio_pmem_config,
> >>> +			size, &vpmem->size);
> >>> +
> >>> +	res.start = vpmem->start;
> >>> +	res.end   = vpmem->start + vpmem->size-1;
> >>> +	vpmem->nd_desc.provider_name = "virtio-pmem";
> >>> +	vpmem->nd_desc.module = THIS_MODULE;
> >>> +
> >>> +	vpmem->nvdimm_bus = nvdimm_bus_register(&vdev->dev,
> >>> +						&vpmem->nd_desc);
> >>> +	if (!vpmem->nvdimm_bus)
> >>> +		goto out_vq;
> >>> +
> >>> +	dev_set_drvdata(&vdev->dev, vpmem->nvdimm_bus);
> >>> +
> >>> +	ndr_desc.res = &res;
> >>> +	ndr_desc.numa_node = nid;
> >>> +	ndr_desc.flush = async_pmem_flush;
> >>> +	set_bit(ND_REGION_PAGEMAP, &ndr_desc.flags);
> >>> +	set_bit(ND_REGION_ASYNC, &ndr_desc.flags);
> >>> +	nd_region = nvdimm_pmem_region_create(vpmem->nvdimm_bus, &ndr_desc);
> >>> +
> >>
> >> I'd drop this empty line.
> > 
> > hmm.
> > 
> 
> The common pattern after allocating something, immediately check for it
> in the next line (like you do throughout this patch ;) )

Right. But rare times when I see space will beauty the code I tend to
add it. Maybe I should not :)

> 
> ...
> >> You are not freeing "vdev->priv".
> > 
> > vdev->priv is vpmem which is allocated using devm API.
> 
> I'm confused. Looking at drivers/virtio/virtio_balloon.c:
> 
> static void virtballoon_remove(struct virtio_device *vdev)
> {
> 	struct virtio_balloon *vb = vdev->priv;
> 
> 	...
> 
> 	kfree(vb);
> }
> 
> I think you should do the same here, vdev->priv is allocated in
> virtio_pmem_probe.
> 
> But maybe I am missing something important here :)

Because virtio_balloon use "kzalloc" for allocation and needs to be freed. 
But virtio pmem uses "devm_kzalloc" which takes care of automatically deleting 
the device memory when associated device is detached.

Thanks,
Pankaj
> 
> >>
> >>> +	nvdimm_bus_unregister(nvdimm_bus);
> >>> +	vdev->config->del_vqs(vdev);
> >>> +	vdev->config->reset(vdev);
> >>> +}
> >>> +
> 
> --
> 
> Thanks,
> 
> David / dhildenb
> 

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