linux-kernel - Re: [RFC PATCH 02/12] On Tue, 23 Sep 2008, David Miller wrote:

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Date:	Sat, 4 Oct 2008 18:24:10 -0700
From:	"Jesse Brandeburg" <jesse.brandeburg@...il.com>
To:	"Thomas Gleixner" <tglx@...utronix.de>
Cc:	"Jiri Kosina" <jkosina@...e.cz>,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>,
	"David Miller" <davem@...emloft.net>, jesse.brandeburg@...el.com,
	linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
	kkeil@...e.de, agospoda@...hat.com, arjan@...ux.intel.com,
	david.graham@...el.com, bruce.w.allan@...el.com,
	john.ronciak@...el.com, chris.jones@...onical.com,
	tim.gardner@...onical.com, airlied@...il.com,
	"Olaf Kirch" <okir@...e.de>,
	"Linus Torvalds" <torvalds@...ux-foundation.org>
Subject: Re: [RFC PATCH 02/12] On Tue, 23 Sep 2008, David Miller wrote:

On Sat, Oct 4, 2008 at 4:02 AM, Thomas Gleixner <tglx@...utronix.de> wrote:
> On Sat, 4 Oct 2008, Jiri Kosina wrote:
>> On Fri, 3 Oct 2008, Jesse Brandeburg wrote:
>> > Our experience is different.  We are also testing with the "protection
>> > patch" reverted.
>> > We see that the problem specifically comes and goes when
>> > removing/adding the use of set_memory_ro/set_memory_rw to the driver.
>>
>> But if this patch (which is an obvious workaround, compared to the other
>> patches which fix real bugs, right?) would be catching some malicious
>> accessess to the mapped EEPROM, there should be stacktraces present in the
>> kernel log, right?

yes, but I think it is just changing timing, i don't see any backtraces either.

> Exactly. The access to a ro region results in a fault. I have nowhere
> seen that trigger, but I can reproduce the trylock() WARN_ON, which
> confirms that there is concurrent access to the NVRAM registers. The
> backtrace pattern is similar to the one you have seen.

are you still getting WARN_ON *with* all the mutex based fixes already applied?

with the mutex patches in place (without protection patch) we are
still reproducing the issue, until we apply the set_memory_ro patch.
I had no luck on friday setting a hardware breakpoint on memory access
with kgdb to catch the writer with a breakpoint.
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