Re: [PATCH] tpm: WARN_ONCE() -> pr_warn_once() in tpm_tis_status()

[Jarkko Sakkinen <jarkko@kernel.org>]

On Tue, Feb 02, 2021 at 09:58:24AM -0800, James Bottomley wrote:
> On Tue, 2021-02-02 at 11:26 -0600, Serge E. Hallyn wrote:
> > On Tue, Feb 02, 2021 at 05:33:17PM +0200, jarkko@kernel.org wrote:
> > > From: Jarkko Sakkinen <jarkko@kernel.org>
> > > 
> > > An unexpected status from TPM chip is not irrecovable failure of
> > > the
> > > kernel. It's only undesirable situation. Thus, change the WARN_ONCE
> > > instance inside tpm_tis_status() to pr_warn_once().
> > > 
> > > In addition: print the status in the log message because it is
> > > actually
> > > useful information lacking from the existing log message.
> > > 
> > > Suggested-by:  Guenter Roeck <linux@roeck-us.net>
> > > Cc: stable@vger.kernel.org
> > > Fixes: 6f4f57f0b909 ("tpm: ibmvtpm: fix error return code in
> > > tpm_ibmvtpm_probe()")
> > > Signed-off-by: Jarkko Sakkinen <jarkko@kernel.org>
> > > ---
> > >  drivers/char/tpm/tpm_tis_core.c | 2 +-
> > >  1 file changed, 1 insertion(+), 1 deletion(-)
> > > 
> > > diff --git a/drivers/char/tpm/tpm_tis_core.c
> > > b/drivers/char/tpm/tpm_tis_core.c
> > > index 431919d5f48a..21f67c6366cb 100644
> > > --- a/drivers/char/tpm/tpm_tis_core.c
> > > +++ b/drivers/char/tpm/tpm_tis_core.c
> > > @@ -202,7 +202,7 @@ static u8 tpm_tis_status(struct tpm_chip *chip)
> > >  		 * acquired.  Usually because tpm_try_get_ops() hasn't
> > >  		 * been called before doing a TPM operation.
> > >  		 */
> > > -		WARN_ONCE(1, "TPM returned invalid status\n");
> > > +		pr_warn_once("TPM returned invalid status: 0x%x\n",
> > > status);
> > >  		return 0;
> > >  	}
> > 
> > Actually in this case I don't understand why _once, especially based
> > on the comment.  Would ratelimited not be better?  So we can see if
> > it happens repeatedly?  Even better would be if we could see when it
> > next gave a valid status after an invalid one.
> 
> The reason was that we're trying to catch and kill paths to the status
> where the locality is incorrect.  If you do some operation that finds
> an incorrect path the likelihood is you'll exercise it more than once,
> but all we need to identify it is the call trace from a single access. 
> The symptom the user space process sees is a TPM timeout, but we still
> have the in-kernel trace to tell us why.

I don't agree with this reasoning. This warn could spun off also from chip
not following TCG spec. The patch does provide the status code, which is
always useful information.

/Jarkko