linux-kernel - Re: [Kgdb-bugreport] [PATCH 4/5] kgdb: Use atomic operators whichuse barriers

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Message-ID: <4BB64CDA.4000405@windriver.com>
Date:	Fri, 02 Apr 2010 15:00:26 -0500
From:	Jason Wessel <jason.wessel@...driver.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
CC:	kgdb-bugreport@...ts.sourceforge.net,
	Will Deacon <will.deacon@....com>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Russell King - ARM Linux <linux@....linux.org.uk>,
	linux-arm@...r.kernel.org
Subject: Re: [Kgdb-bugreport] [PATCH 4/5] kgdb: Use atomic operators whichuse
 barriers

On 04/02/2010 02:47 PM, Linus Torvalds wrote:
>
>> From: Jason Wessel <jason.wessel@...driver.com>
>> Subject: [PATCH] kgdb: Use atomic operators which use barriers
>>
>> The cpu_relax() does not mandate that there is an smp memory barrier.
>> As a result on the arm smp architecture the kernel debugger can hang
>> on entry from time to time, as shown by the kgdb regression tests.
>>     
>
> Now your changelog makes no sense any more.
>   

It is revised now and pushed.  Regression testing on the HW I have has
passed as well now.

For the series the pull looks like:

 drivers/misc/kgdbts.c |    6 ++
 kernel/kgdb.c         |  205
+++++++++++++++++++++++++------------------------
 2 files changed, 109 insertions(+), 102 deletions(-)


Thanks,
Jason.


---
From: Jason Wessel <jason.wessel@...driver.com>
Subject: [PATCH] kgdb: use atomic_inc and atomic_dec instead of atomic_set

Memory barriers should be used for the kgdb cpu synchronization.  The
atomic_set() does not imply a memory barrier.

Reported-by: Will Deacon <will.deacon@....com>
Signed-off-by: Jason Wessel <jason.wessel@...driver.com>
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