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Date:   Tue, 2 Feb 2021 18:17:34 +0200
From:   Jarkko Sakkinen <jarkko@kernel.org>
To:     James Bottomley <James.Bottomley@hansenpartnership.com>
Cc:     Guenter Roeck <linux@roeck-us.net>,
        =?utf-8?Q?=C5=81ukasz?= Majczak <lma@semihalf.com>,
        Peter Huewe <peterhuewe@gmx.de>,
        Jason Gunthorpe <jgg@ziepe.ca>,
        linux-integrity@vger.kernel.org, linux-kernel@vger.kernel.org,
        Radoslaw Biernacki <rad@semihalf.com>,
        Marcin Wojtas <mw@semihalf.com>,
        Alex Levin <levinale@google.com>
Subject: Re: [PATCH] tpm_tis: Add missing start/stop_tpm_chip calls
Message-ID: <YBl7HlcgPSX0qRHy@kernel.org>
References: <20210123014247.989368-1-lma@semihalf.com>
 <20210125171846.GA31929@roeck-us.net>
 <CAFJ_xboNDcp-XrxfbrBjqTWjLZUdVWe1OJi4KK==ij+yivFeHA@mail.gmail.com>
 <YBSTOrlgTPpzoblY@kernel.org>
 <7a702108-ec9e-b2e2-be89-3590437c0eb5@roeck-us.net>
 <bf4564a2f4f761a4c0a00857c7dc346fc43bcd92.camel@HansenPartnership.com>
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On Sat, Jan 30, 2021 at 04:41:13PM -0800, James Bottomley wrote:
> On Sat, 2021-01-30 at 15:49 -0800, Guenter Roeck wrote:
> > On 1/29/21 2:59 PM, Jarkko Sakkinen wrote:
> > > On Tue, Jan 26, 2021 at 04:46:07PM +0100, Łukasz Majczak wrote:
> > > > Hi Jarkko, Guenter
> > > > 
> > > > Yes, here are the logs when failure occurs -
> > > > https://gist.github.com/semihalf-majczak-lukasz/1575461f585f1e7fb1e9366b8eceaab9
> > > > Look for a phrase "TPM returned invalid status"
> > > > 
> > > > Guenter - good suggestion - I will try to keep it as tight as
> > > > possible.
> > > > 
> > > > Best regards,
> > > > Lukasz
> > > 
> > > Is it possible for you try out with linux-next? Thanks. It's a
> > > known issue, which ought to be fixed by now.
> > > 
> > > The log message is harmless, it'a warning not panic, and does not
> > > endanger system stability. WARN()'s always dump stack trace. No
> > > oops is happening.
> > > 
> > 
> > There is a note in the kernel documentation which states:
> > 
> > Note that the WARN()-family should only be used for "expected to
> > be unreachable" situations. If you want to warn about "reachable
> > but undesirable" situations, please use the pr_warn()-family of
> > functions.
> 
> It fits the definition.  The warning only triggers if the access is in
> the wrong locality, which should be impossible, so the warning should
> be unreachable.

It's an overkill. Even in perfectly working kernel it's not impossible, as
sometimes hardware gives faulty data. I think that it also lacks the useful
information i.e. the status code.

I would useful WARN() only if the driver state could suffer. In this case
it doesn't. It only results failing transfer but kernel state is still
legit.

/Jarkko
>