From: Jason Gunthorpe <jgunthorpe-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
To: Jarkko Sakkinen
<jarkko.sakkinen-VuQAYsv1563Yd54FQh9/CA@public.gmane.org>
Cc: "tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org"
<tpmdd-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>,
"linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org"
<linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>
Subject: Re: [PATCH] tpm: don't destroy chip device prematurely
Date: Wed, 5 Oct 2016 10:27:41 -0600 [thread overview]
Message-ID: <20161005162741.GA18636@obsidianresearch.com> (raw)
In-Reply-To: <20161005100234.GA20851-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
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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WARNING: multiple messages have this Message-ID (diff)
From: Jason Gunthorpe <jgunthorpe@obsidianresearch.com>
To: Jarkko Sakkinen <jarkko.sakkinen@linux.intel.com>
Cc: "Winkler, Tomas" <tomas.winkler@intel.com>,
"tpmdd-devel@lists.sourceforge.net"
<tpmdd-devel@lists.sourceforge.net>,
"linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tpm: don't destroy chip device prematurely
Date: Wed, 5 Oct 2016 10:27:41 -0600 [thread overview]
Message-ID: <20161005162741.GA18636@obsidianresearch.com> (raw)
In-Reply-To: <20161005100234.GA20851@intel.com>
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
next prev parent reply other threads:[~2016-10-05 16:27 UTC|newest]
Thread overview: 52+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-10-02 7:39 [PATCH] tpm: don't destroy chip device prematurely Tomas Winkler
[not found] ` <1475393971-12715-1-git-send-email-tomas.winkler-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2016-10-02 10:17 ` Jarkko Sakkinen
2016-10-02 10:17 ` Jarkko Sakkinen
[not found] ` <20161002101755.GA25844-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2016-10-02 10:24 ` Jarkko Sakkinen
2016-10-02 10:24 ` Jarkko Sakkinen
[not found] ` <20161002102455.GA27464-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2016-10-02 21:21 ` Jason Gunthorpe
2016-10-02 21:21 ` Jason Gunthorpe
[not found] ` <20161002212126.GA25872-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2016-10-03 7:05 ` Winkler, Tomas
2016-10-03 7:05 ` Winkler, Tomas
[not found] ` <5B8DA87D05A7694D9FA63FD143655C1B542F466B-Jy8z56yoSI8MvF1YICWikbfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2016-10-03 7:38 ` Winkler, Tomas
2016-10-03 7:38 ` Winkler, Tomas
[not found] ` <5B8DA87D05A7694D9FA63FD143655C1B542F46C1-Jy8z56yoSI8MvF1YICWikbfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2016-10-03 12:42 ` Jarkko Sakkinen
2016-10-03 12:42 ` Jarkko Sakkinen
2016-10-03 16:03 ` Jason Gunthorpe
[not found] ` <20161003160308.GA6801-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2016-10-03 17:30 ` Winkler, Tomas
2016-10-03 17:30 ` Winkler, Tomas
2016-10-03 12:48 ` Jarkko Sakkinen
[not found] ` <20161003124836.GE9990-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2016-10-04 5:19 ` Jarkko Sakkinen
2016-10-04 5:19 ` Jarkko Sakkinen
2016-10-04 16:47 ` Jason Gunthorpe
2016-10-04 21:55 ` Winkler, Tomas
2016-10-04 23:10 ` Jason Gunthorpe
[not found] ` <20161004231057.GA20062-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2016-10-05 7:48 ` Winkler, Tomas
2016-10-05 7:48 ` Winkler, Tomas
[not found] ` <5B8DA87D05A7694D9FA63FD143655C1B542F5084-Jy8z56yoSI8MvF1YICWikbfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2016-10-05 15:15 ` Jarkko Sakkinen
2016-10-05 15:15 ` Jarkko Sakkinen
2016-10-05 16:37 ` Jason Gunthorpe
2016-10-05 17:11 ` Jason Gunthorpe
2016-10-05 20:09 ` Winkler, Tomas
2016-10-05 21:16 ` Jason Gunthorpe
2016-10-06 0:43 ` Winkler, Tomas
[not found] ` <5B8DA87D05A7694D9FA63FD143655C1B542F561B-Jy8z56yoSI8MvF1YICWikbfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2016-10-06 2:07 ` Jason Gunthorpe
2016-10-06 2:07 ` Jason Gunthorpe
[not found] ` <20161006020748.GA17479-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2016-10-07 14:24 ` Winkler, Tomas
2016-10-07 14:24 ` Winkler, Tomas
2016-10-07 19:17 ` Jason Gunthorpe
[not found] ` <20161007191724.GA28795-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2016-10-07 20:10 ` Winkler, Tomas
2016-10-07 20:10 ` Winkler, Tomas
[not found] ` <5B8DA87D05A7694D9FA63FD143655C1B542F625A-Jy8z56yoSI8MvF1YICWikbfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2016-10-08 10:47 ` Jarkko Sakkinen
2016-10-08 10:47 ` Jarkko Sakkinen
2016-10-05 10:02 ` Jarkko Sakkinen
[not found] ` <20161005100234.GA20851-ral2JQCrhuEAvxtiuMwx3w@public.gmane.org>
2016-10-05 16:27 ` Jason Gunthorpe [this message]
2016-10-05 16:27 ` Jason Gunthorpe
2016-10-06 11:23 ` Jarkko Sakkinen
2016-10-06 16:22 ` Jason Gunthorpe
[not found] ` <20161006162245.GF1224-ePGOBjL8dl3ta4EC/59zMFaTQe2KTcn/@public.gmane.org>
2016-10-06 16:46 ` Jarkko Sakkinen
2016-10-06 16:46 ` Jarkko Sakkinen
2016-10-05 10:09 ` Jarkko Sakkinen
2016-10-03 16:00 ` Jason Gunthorpe
2016-10-03 17:16 ` Winkler, Tomas
[not found] ` <5B8DA87D05A7694D9FA63FD143655C1B542F474C-Jy8z56yoSI8MvF1YICWikbfspsVTdybXVpNB7YpNyf8@public.gmane.org>
2016-10-03 17:30 ` Jason Gunthorpe
2016-10-03 17:30 ` Jason Gunthorpe
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