Commit a7e30b8d authored Oct 10, 2007 by Philippe Rétornaz Committed by Haavard Skinnemoen Oct 11, 2007

[AVR32] Fix random segfault with preemption

As explained on:
http://www.avrfreaks.net/index.php?nameÿphpBB2&fileÿewtopic&tS307


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 Rétornaz <philippe.retornaz@epfl.ch>
Signed-off-by: Haavard Skinnemoen <hskinnemoen@atmel.com>

parent bb7aa6d4

arch/avr32/kernel/entry-avr32b.S

+25 −1

Original line number	Diff line number	Diff line
		@@ -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 +682,16 @@ 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