linux-kernel - Re: [PATCH] tpm: Make chip->{status,cancel,req

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Message-ID: <56428ff1ac4355482df881e6226518c2a62beb6d.camel@HansenPartnership.com>
Date: Thu, 27 Mar 2025 10:12:36 -0400
From: James Bottomley <James.Bottomley@...senPartnership.com>
To: Jarkko Sakkinen <jarkko@...nel.org>, Stefano Garzarella
	 <sgarzare@...hat.com>
Cc: linux-integrity@...r.kernel.org, Sumit Garg <sumit.garg@...nel.org>, 
 Jens Wiklander <jens.wiklander@...aro.org>, Jarkko Sakkinen
 <jarkko.sakkinen@...nsys.com>, Peter Huewe <peterhuewe@....de>, Jason
 Gunthorpe <jgg@...pe.ca>,  linux-kernel@...r.kernel.org
Subject: Re: [PATCH] tpm: Make chip->{status,cancel,req_canceled} opt

On Thu, 2025-03-27 at 15:23 +0200, Jarkko Sakkinen wrote:
> On Thu, Mar 27, 2025 at 10:58:00AM +0100, Stefano Garzarella wrote:
[...]
> > > @@ -65,6 +89,7 @@ static ssize_t tpm_try_transmit(struct tpm_chip
> > > *chip, void *buf, size_t bufsiz)
> > > 	ssize_t len = 0;
> > > 	u32 count, ordinal;
> > > 	unsigned long stop;
> > > +	u8 status;
> > 
> > Why move `status` out of the do/while block?
> 
> I'm not a huge fan of stack allocations inside blocks, unless there
> is a particular reason to do so.

The move to scope based locking and freeing in cleanup.h necessitates
using scope based variables as well, so they're something we all have
to embrace.  They're also useful to tell the compiler when it can
reclaim the variable and they often create an extra stack frame that
allows the reclaim to be effective (even if the compiler can work out
where a variable is no longer reference, the space can't be reclaimed
if it's in the middle of an in-use stack frame).  I'd say the rule of
thumb should be only do something like this if it improves readability
or allows you to remove an additional block from the code.

Regards,

James