linux-kernel - Re: [PATCH 26/44] drivers/scsi: use min() instead of min

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Message-ID: <20251120184409.67db1c25@pumpkin>
Date: Thu, 20 Nov 2025 18:44:09 +0000
From: David Laight <david.laight.linux@...il.com>
To: Bart Van Assche <bvanassche@....org>
Cc: linux-kernel@...r.kernel.org, linux-scsi@...r.kernel.org, "James E.J.
 Bottomley" <James.Bottomley@...senPartnership.com>, "Martin K. Petersen"
 <martin.petersen@...cle.com>
Subject: Re: [PATCH 26/44] drivers/scsi: use min() instead of min_t()

On Wed, 19 Nov 2025 15:09:02 -0800
Bart Van Assche <bvanassche@....org> wrote:

> On 11/19/25 2:41 PM, david.laight.linux@...il.com wrote:
> > From: David Laight <david.laight.linux@...il.com>
> > 
> > min_t(unsigned int, a, b) casts an 'unsigned long' to 'unsigned int'.
> > Use min(a, b) instead as it promotes any 'unsigned int' to 'unsigned long'
> > and so cannot discard significant bits.
> > 
> > In this case the 'unsigned long' value is small enough that the result
> > is ok.
> > 
> > Detected by an extra check added to min_t().
> > 
> > Signed-off-by: David Laight <david.laight.linux@...il.com>
> > ---
> >   drivers/scsi/hosts.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
> > index 17173239301e..b15896560cf6 100644
> > --- a/drivers/scsi/hosts.c
> > +++ b/drivers/scsi/hosts.c
> > @@ -247,7 +247,7 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
> >   	shost->dma_dev = dma_dev;
> >   
> >   	if (dma_dev->dma_mask) {
> > -		shost->max_sectors = min_t(unsigned int, shost->max_sectors,
> > +		shost->max_sectors = min(shost->max_sectors,
> >   				dma_max_mapping_size(dma_dev) >> SECTOR_SHIFT);
> >   	}  
> 
> So instead of the type cast performed by min_t() potentially discarding
> bits, the assignment potentially discards bits. I'm not sure this is an
> improvement.

The assignment cant discard bits because shost->max_sectors is also on the RHS.
In any case you'd need a 2TB mapping size to get an error.
That probably cant happen for other reasons.

The patch is remove a false positive for a check added to min_t(T, a, b)
that sizeof (b) <= sizeof (T).

	David

> 
> Thanks,
> 
> Bart.
>