[RFC/PATCH v4 7/7] ARM: ARM11 MPCore: cpu_v6_set_pte_ext is not preempt safe

[Nicolas Pitre]

On Tue, 18 Oct 2011, gdavis at mvista.com wrote:

> @@ -122,7 +122,22 @@ ENTRY(cpu_v6_switch_mm)
>  
>  ENTRY(cpu_v6_set_pte_ext)
>  #ifdef CONFIG_MMU
> +#if	defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
> +	stmdb	sp!, {r4, r5}
> +	get_thread_info r5
> +	ldr	r4, [r5, #TI_PREEMPT]	@ get preempt count
> +	add	r3, r4, #1		@ increment it
> +	str	r3, [r5, #TI_PREEMPT]	@ disable preempt
> +#endif
>  	armv6_set_pte_ext cpu_v6
> +#if	defined(CONFIG_SMP) && defined(CONFIG_PREEMPT)
> +	str	r4, [r5, #TI_PREEMPT]	@ restore preempt count
> +	teq	r4, #0			@ preempt count == 0?
> +	ldreq	r4, [r5, #TI_FLAGS]	@ load flags if yes
> +	tst	r4, #_TIF_NEED_RESCHED	@ need resched?
> +	ldmia	sp!, {r4, r5}
> +	bne	preempt_schedule	@ ret via preempt_schedule
> +#endif

Same issue as previous patch.

Wouldn't it be better if you disabled interrupts around the small 
critical region within armv6_set_pte_ext instead?  That would certainly 
be a lighter solution.  Something like:

diff --git a/arch/arm/mm/proc-macros.S b/arch/arm/mm/proc-macros.S
index 307a4def8d..9bc2dbfe4e 100644
--- a/arch/arm/mm/proc-macros.S
+++ b/arch/arm/mm/proc-macros.S
@@ -167,8 +167,11 @@
 	tstne	r1, #L_PTE_PRESENT
 	moveq	r3, #0
 
+	mrs	r2, cpsr
+	cpsid	i
 	str	r3, [r0]
 	mcr	p15, 0, r0, c7, c10, 1		@ flush_pte
+	msr	cpsr_c, r2
 	.endm


Nicolas