linux-kernel - Re: [PATCH v3 4/8] blk-mp: introduce blk_mq_hctx_map

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Message-ID: <2024111215-jury-unlighted-3953@gregkh>
Date: Tue, 12 Nov 2024 16:42:40 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: Daniel Wagner <dwagner@...e.de>
Cc: Daniel Wagner <wagi@...nel.org>, Jens Axboe <axboe@...nel.dk>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	"Michael S. Tsirkin" <mst@...hat.com>,
	Jason Wang <jasowang@...hat.com>,
	Xuan Zhuo <xuanzhuo@...ux.alibaba.com>,
	Eugenio Pérez <eperezma@...hat.com>,
	"Martin K. Petersen" <martin.petersen@...cle.com>,
	Keith Busch <kbusch@...nel.org>, Christoph Hellwig <hch@....de>,
	Sagi Grimberg <sagi@...mberg.me>, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	virtualization@...ts.linux.dev, linux-scsi@...r.kernel.org,
	megaraidlinux.pdl@...adcom.com, mpi3mr-linuxdrv.pdl@...adcom.com,
	MPT-FusionLinux.pdl@...adcom.com, storagedev@...rochip.com,
	linux-nvme@...ts.infradead.org
Subject: Re: [PATCH v3 4/8] blk-mp: introduce blk_mq_hctx_map_queues

On Tue, Nov 12, 2024 at 04:33:09PM +0100, Daniel Wagner wrote:
> On Tue, Nov 12, 2024 at 02:58:43PM +0100, Greg Kroah-Hartman wrote:
> > > +void blk_mq_hctx_map_queues(struct blk_mq_queue_map *qmap,
> > > +			    struct device *dev, unsigned int offset)
> > > +
> > > +{
> > > +	const struct cpumask *mask;
> > > +	unsigned int queue, cpu;
> > > +
> > > +	if (!dev->bus->irq_get_affinity)
> > > +		goto fallback;
> > 
> > I think this is better than hard-coding it, but are you sure that the
> > bus will always be bound to the device here so that you have a valid
> > bus-> pointer?
> 
> No, I just assumed the bus pointer is always valid. If it is possible to
> have a device without a bus, than I'll better extend the condition to
> 
> 	if (!dev->bus || !dev->bus->irq_get_affinity)
>         	goto fallback;

I don't know if it's possible as I don't know what codepaths are calling
this, it was hard to unwind.  But you should check "just to be safe" :)

thanks,

greg k-h