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.
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 R?tornaz <[email protected]>
---
arch/avr32/kernel/entry-avr32b.S | 27 ++++++++++++++++++++++++++-
1 file changed, 26 insertions(+), 1 deletion(-)
diff --git a/arch/avr32/kernel/entry-avr32b.S b/arch/avr32/kernel/entry-avr32b.S
index 42657f1..f7f2530 100644
--- a/arch/avr32/kernel/entry-avr32b.S
+++ b/arch/avr32/kernel/entry-avr32b.S
@@ -159,11 +159,18 @@ handle_vmalloc_miss:
.section .scall.text,"ax",@progbits
system_call:
+#ifdef CONFIG_PREEMPT
+ mask_interrupts
+#endif
pushm r12 /* r12_orig */
stmts --sp, r0-lr
- zero_fp
+
mfsr r0, SYSREG_RAR_SUP
mfsr r1, SYSREG_RSR_SUP
+#ifdef CONFIG_PREEMPT
+ unmask_interrupts
+#endif
+ zero_fp
stm --sp, r0-r1
/* check for syscall tracing */
@@ -638,6 +645,13 @@ irq_level\level:
stmts --sp,r0-lr
mfsr r8, rar_int\level
mfsr r9, rsr_int\level
+
+#ifdef CONFIG_PREEMPT
+ sub r11, pc, (. - system_call)
+ cp.w r11,r8
+ breq 4f
+#endif
+
pushm r8-r9
mov r11, sp
@@ -668,6 +682,17 @@ irq_level\level:
sub sp, -4 /* ignore r12_orig */
rete
+#ifdef CONFIG_PREEMPT
+4:
+ mask_interrupts
+ mfsr r8,rsr_int\level
+ sbr r8, 16
+ mtsr rsr_int\level, r8
+ ldmts sp++,r0-lr
+ sub sp, -4 /* ignore r12_orig */
+ rete
+#endif
+
2: get_thread_info r0
ld.w r1, r0[TI_flags]
bld r1, TIF_CPU_GOING_TO_SLEEP
On Wed, 10 Oct 2007 18:52:24 -0400
Philippe Rétornaz <[email protected]> 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 <[email protected]>
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