linux-kernel - Re: [PATCH] tpm_tis: Add missing start/stop_tpm

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Date:   Sat, 30 Jan 2021 16:41:13 -0800
From:   James Bottomley <James.Bottomley@...senPartnership.com>
To:     Guenter Roeck <linux@...ck-us.net>,
        Jarkko Sakkinen <jarkko@...nel.org>,
        Łukasz Majczak <lma@...ihalf.com>
Cc:     Peter Huewe <peterhuewe@....de>, Jason Gunthorpe <jgg@...pe.ca>,
        linux-integrity@...r.kernel.org, linux-kernel@...r.kernel.org,
        Radoslaw Biernacki <rad@...ihalf.com>,
        Marcin Wojtas <mw@...ihalf.com>,
        Alex Levin <levinale@...gle.com>
Subject: Re: [PATCH] tpm_tis: Add missing start/stop_tpm_chip calls

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.

James

> It seems to me that "harmless" doesn't really fit the expected
> use of WARN(). Should it possibly be converted to pr_warn() ?