linux-kernel - Re: [Regression 4.15-rc2] New messages `tpm tpm0: A TPM error (2314) occurred continue selftest`

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Date:   Fri, 8 Dec 2017 08:56:41 -0700
From:   Jason Gunthorpe <jgg@...pe.ca>
To:     Alexander.Steffen@...ineon.com
Cc:     pmenzel@...gen.mpg.de, linux-integrity@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [Regression 4.15-rc2] New messages `tpm tpm0: A TPM error (2314)
 occurred continue selftest`

On Fri, Dec 08, 2017 at 12:14:04PM +0000, Alexander.Steffen@...ineon.com wrote:

> Is it really that ugly? I still need delay_msec to increase the
> delay each round. I can see the benefit of your suggestion when it
> is important to get the timing exactly right (and also account for
> time spent elsewhere, when our code might not be executing). But in
> this case having delays that are approximately right (or longer than
> intended) is sufficient.

For timeouts like this we really need to be above the TPM specified
delay in all cases, even if usleep_range selected something
smaller/larger.. The only way to do that is with an absolute timeout..


> Anyway, from the log messages it is clear that tpm_msleep got called
> seven times with delays of 20/40/80/160/320/640/1280ms. But still
> all timestamps lie within the same second. How can this be with a
> cumulated delay of ~2.5s?

Yes, that does seem to be the bug, our sleep function doesn't work
aynmore for some reason :|

> Also, I've just noticed that despite the name tpm_msleep calls
> usleep_range, not msleep. Can this have an influence? Should
> tpm_msleep call msleep for longer delays, as suggested by
> Documentation/timers/timers-howto.txt?

This change was introduced recently and is probably the source of this
regression.

Jason