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

From Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
Newsgroups linux.kernel
Subject Re: [PATCH] tpm: don't destroy chip device prematurely
Date 2016-10-05 18:30 +0200
Message-ID <soXeV-3hV-5@gated-at.bofh.it> (permalink)
References (4 earlier) <so5xT-Vq-1@gated-at.bofh.it> <soaQV-4YM-9@gated-at.bofh.it> <soqsF-6wU-1@gated-at.bofh.it> <soB4J-5is-11@gated-at.bofh.it> <soRjb-7Pg-1@gated-at.bofh.it>
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On Wed, Oct 05, 2016 at 01:02:34PM +0300, Jarkko Sakkinen wrote:

> I'll repeat my question: what worse can happen than returning -EPIPE?  I
> though the whole rw lock scheme was introduced just for this purpose.

I thought I explained this, if device_del is moved after ops = null
then if sysfs looses the race it will oops the kernel. device_del hard
fences sysfs.

> Why there's even that branch in tpm-dev.c if it's so bad to let it
> happen?

Because cdev_del and device_del do not guarentee that the cdev is
fenced. They just prevent new calls into open(). So the branch in
tpm-dev.c is necessary to avoid a kernel oops if user space holds the
fd open across unregister.

It is the same sitatuion you identified in the securityfs discussion -
user space holding the fd open across a driver unregister.

Jason

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Thread

[PATCH] tpm: don't destroy chip device prematurely Tomas Winkler <tomas.winkler@intel.com> - 2016-10-02 09:50 +0200
  Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-02 12:20 +0200
    Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-02 12:30 +0200
      Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-02 23:30 +0200
        RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-03 09:10 +0200
          RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-03 09:40 +0200
            Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-03 14:50 +0200
              Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-03 18:10 +0200
                RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-03 19:40 +0200
          Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-03 14:50 +0200
            Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-04 07:30 +0200
              Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-04 18:50 +0200
                RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-05 00:00 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-05 01:20 +0200
                RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-05 09:50 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-05 17:20 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-05 18:40 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-05 19:20 +0200
                RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-05 22:10 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-05 23:20 +0200
                RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-06 02:50 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-06 04:10 +0200
                RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-07 16:30 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-07 21:20 +0200
                RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-07 22:20 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-08 12:50 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-05 12:10 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-05 18:30 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-06 13:30 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-06 18:30 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-06 18:50 +0200
                Re: [PATCH] tpm: don't destroy chip device prematurely Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com> - 2016-10-05 12:10 +0200
          Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-03 18:10 +0200
            RE: [PATCH] tpm: don't destroy chip device prematurely "Winkler, Tomas" <tomas.winkler@intel.com> - 2016-10-03 19:20 +0200
              Re: [PATCH] tpm: don't destroy chip device prematurely Jason Gunthorpe <jgunthorpe@obsidianresearch.com> - 2016-10-03 19:40 +0200

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