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SubjectRe: [PATCH] AVR32: Fix random segfault with preemption
On Wed, 10 Oct 2007 18:52:24 -0400
Philippe Rétornaz <philippe.retornaz@epfl.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@epfl.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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