linux-kernel - Re: [tpmdd-devel] [PATCH] tpm: fix multiple race conditions in tpm

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Date:	Wed, 22 Oct 2014 13:05:33 +0300
From:	Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Peter Huewe <peterhuewe@....de>, Ashley Lai <ashley@...leylai.com>,
	Marcel Selhorst <tpmdd@...horst.net>,
	tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org
Subject: Re: [tpmdd-devel] [PATCH] tpm: fix multiple race conditions in
 tpm_ppi.c

On Tue, Oct 21, 2014 at 03:02:15PM -0600, Jason Gunthorpe wrote:
> On Tue, Oct 21, 2014 at 11:42:51PM +0300, Jarkko Sakkinen wrote:
> 
> > > Personally, I'd sequence this commit right after your 'tpm: two-phase
> > > chip management functions' commit because it makes it much saner (no
> > > half step toward the new functions). I assume this is a theoretical
> > > problem? Or do you have a two TPM system?
> > 
> > This has realized in Intel NUCs where there is PTT and dTPM module. Even
> > when PTT is selected there is still ACPI device for dTPM so three is a
> > race condition and PPI is unusable. I think that it's not good that code is
> > not robust enough to deal with this.
> 
> Oh OK, you should probably explain in the commit log that this is a
> bug fix that impacts real hardware, that qualifies it for the -stable
> tree.
> 
> Assuming two-phase commit is nearly ready to go, I'd still sequence
> this fix after two-phase for mainline and then use this patch as-is
> for the 3.17 -stable backport of the mainline commit.

OK, makes sense. I'll try to get this done tonight.

> > Even if you forget the race condition it feels waste to lookup a handle
> > that is already known.
> 
> There is no doubt that this new arrangement is much better than what
> was there before!
> 
> Thanks,
> Jason

/Jarkko
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