linux-kernel - Re: [PATCH] tpm/tpm_i2c_infineon: ensure no ongoing commands on shutdown

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Date:   Fri, 13 Jan 2017 17:28:57 -0700
From:   Jason Gunthorpe <jgunthorpe@...idianresearch.com>
To:     Andrey Pronin <apronin@...omium.org>
Cc:     Peter Huewe <peterhuewe@....de>,
        Marcel Selhorst <tpmdd@...horst.net>,
        Jarkko Sakkinen <jarkko.sakkinen@...ux.intel.com>,
        tpmdd-devel@...ts.sourceforge.net, linux-kernel@...r.kernel.org,
        semenzato@...omium.org, groeck@...omium.org
Subject: Re: [PATCH] tpm/tpm_i2c_infineon: ensure no ongoing commands on
 shutdown

On Fri, Jan 13, 2017 at 04:09:54PM -0800, Andrey Pronin wrote:
> Resetting TPM while processing a command may lead to issues
> on the next boot. Ensure that we don't have any ongoing
> commands, and that no further commands can be sent to the chip
> by unregistering the device in the shutdown handler.
> tpm_chip_unregister() waits for the completion of an ongoing
> command, if any, and then clears out chip->ops and unregisters
> sysfs entities.

Unregistering in a shutdown handler seems very strange, it also waits
for userspace things, so I wonder if it could be problematic?

Maybe just use

   down_write(&chip->ops_sem);
   chip->ops = NULL;
   up_write(&chip->ops_sem);

In the shutdown handler?

Jason