linux-kernel - Re: [PATCH] tpm: don't destroy chip device prematurely

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Date:   Thu, 6 Oct 2016 19:46:21 +0300
From:   Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>
To:     Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:     "Winkler, Tomas" <tomas.winkler@...el.com>,
        "tpmdd-devel@...ts.sourceforge.net" 
        <tpmdd-devel@...ts.sourceforge.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] tpm: don't destroy chip device prematurely

On Thu, Oct 06, 2016 at 10:22:45AM -0600, Jason Gunthorpe wrote:
> On Thu, Oct 06, 2016 at 02:23:57PM +0300, Jarkko Sakkinen wrote:
> 
> > I think that they should be fenced then for the sake of consistency.
> > I do not see why sysfs code is privileged not to do fencing while other
> > peers have to do it.
> 
> Certainly the locking could be changed, but it would be nice to have a
> reason other than aesthetics.
> 
> sysfs is not unique, we also do not grab the rwlock lock during any
> commands executed as part of probe. There are basically two locking
> regimes - stuff that is proven to by synchronous with probe/remove
> (sysfs, probe cmds) and everything else (kapi, cdev)
> 
> Further, the current sysfs implementation is nice and sane: the file
> accesses cannot fail with ENODEV. That is a useful concrete property
> and I don't think we should change it without a good reason.

The last point is certainly legit. I think it even might deserve a
comment of its own in tpm_del_char_device.

I think I have a good idea now what to do. Hold on for RFC patch.

> Jason

/Jarkko