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

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Message-ID: <Z-VpjSZSMOk73_Dg@kernel.org>
Date: Thu, 27 Mar 2025 17:06:53 +0200
From: Jarkko Sakkinen <jarkko@...nel.org>
To: James Bottomley <James.Bottomley@...senpartnership.com>
Cc: Stefano Garzarella <sgarzare@...hat.com>,
	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, Mar 27, 2025 at 05:00:11PM +0200, Jarkko Sakkinen wrote:
> On Thu, Mar 27, 2025 at 10:12:36AM -0400, James Bottomley wrote:
> > 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.
> 
> Reclaiming here is only shift in the frame pointer, nothing to do with
> reclaiming resources or freeing locks. Consolidating value state into
> single location does improve readability as far as I'm concerned.

Anyhow, I reverted that change given the feedback :-)

Since I'm late sending PR, I'll put this patch to my 6.15 PR.

BR, Jarkko