On Fri, Jul 11, 2014 at 10:10:13AM +0100, Sebastian Hesselbarth wrote:
> commit 431a84b1a4f7d1a0085d5b91330c5053cc8e8b12
> ("ARM: 8034/1: Disable preemption in iwmmxt_task_enable()")
> introduced macros {inc,dec}_preempt_count to iwmmxt_task_enable
> to make it run with preemption disabled.
>
> Unfortunately, other functions in iwmmxt.S also use concan_{save,dump,load}
> sections located in iwmmxt_task_enable() to deal with iWMMXt coprocessor.
> This causes an unbalanced preempt_count due to excessive dec_preempt_count
> and destroyed return addresses in callers of concan_ labels due to a register
> collision:
Indeed, I missed this part completely.
> --- a/arch/arm/kernel/iwmmxt.S
> +++ b/arch/arm/kernel/iwmmxt.S
> @@ -94,13 +94,19 @@ ENTRY(iwmmxt_task_enable)
>
> mrc p15, 0, r2, c2, c0, 0
> mov r2, r2 @ cpwait
> + bl concan_save
>
> - teq r1, #0 @ test for last ownership
> - mov lr, r9 @ normal exit from exception
> - beq concan_load @ no owner, skip save
> +#ifdef CONFIG_PREEMPT_COUNT
> + get_thread_info r10
> +#endif
> +4: dec_preempt_count r10, r3
> + mov pc, r9 @ normal exit from exception
>
> concan_save:
>
> + teq r1, #0 @ test for last ownership
> + beq concan_load @ no owner, skip save
> +
> tmrc r2, wCon
>
> @ CUP? wCx
> @@ -175,10 +181,6 @@ concan_load:
> tmcr wCon, r2
>
> 3:
> -#ifdef CONFIG_PREEMPT_COUNT
> - get_thread_info r10
> -#endif
> -4: dec_preempt_count r10, r3
> mov pc, lr
It looks fine to me. One optimisation you could do is to replace a
couple of beq 3f with moveq pc, lr.
--
Catalin
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