linux-kernel - Re: [PATCH] AVR32: Fix random segfault with preemption

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Message-ID: <20071011102454.4ff0225f@dhcp-255-175.norway.atmel.com>
Date:	Thu, 11 Oct 2007 10:24:54 +0200
From:	Haavard Skinnemoen <hskinnemoen@...el.com>
To:	Philippe Rétornaz <philippe.retornaz@...l.ch>
Cc:	linux-kernel@...r.kernel.org, kernel@...32linux.org
Subject: Re: [PATCH] AVR32: Fix random segfault with preemption

On Wed, 10 Oct 2007 18:52:24 -0400
Philippe Rétornaz <philippe.retornaz@...l.ch> wrote:

> As explained on:
> http://www.avrfreaks.net/index.php?name=PNphpBB2&file=viewtopic&t=53307
> If the current process is preempted before it can copy RAR_SUP and
> RSR_SUP both register are lost and the process will segfault as soon
> as it return from the syscall since the return adress will be
> corrupted. 
> 
> This patch disable IRQ as soon as we enter the syscall path and
> reenable them when the copy is done. 
> 
> In the interrupt handlers, check if we are interrupting the srrf
> instruction, if so disable interrupts and return. The interrupt
> handler will be re-called immediatly when the interrupts are
> reenabled.

Just to make it clear: It will disable interrupts in the return
context, so interrupts will be disabled when the interrupt handler
returns.

> After some stressing workload:
> - find / > /dev/null in loop
> - top (in ssh)
> - ping -f avr32
> 
> The segfaults are not seen anymore.
> 
> Signed-off-by: Philippe Rétornaz <philippe.retornaz@...l.ch>

Nice work. The patch looks correct as far as I can tell, so I think
I'll merge it as soon as possible, and perhaps enable CONFIG_PREEMPT in
the defconfig, to give it some more exposure.

Thanks!

Håvard
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