Re: [PATCH 10/10] ARM: FIQ: Get rid of init_FIQ()

Alexander Shiyan
2012-11-23T03:51:30Z

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> The function only saves initial arch-specific "no FIQ" instruction, by
> placing the code into set_fiq_handler() we can:
>
> - Have less code and logic in the platform-specific files;
> - Have the code that manages FIQ vector overwriting in one place, i.e.
> don't spread the logic around.
>
> p.s. Also, I noticed that we saved no_fiq_insn w/o bothering about
> !CONFIG_CPU_USE_DOMAINS case, but set_fiq_handler() handles this case
> specifically. I wonder, was that on purpose, e.g. it does not matter for
> init_FIQ(), or it was just overlooked? In the latter case, the patch fixes
> the issue.
...
> diff --git a/arch/arm/kernel/fiq.c b/arch/arm/kernel/fiq.c
> index 9bf3a60..3602df6 100644
> --- a/arch/arm/kernel/fiq.c
> +++ b/arch/arm/kernel/fiq.c
> @@ -49,6 +49,7 @@
> #include <asm/mach/irq.h>
>
> static unsigned long no_fiq_insn;
> +static int got_no_fiq_insn;
>
> /* Default reacquire function
> * - we always relinquish FIQ control
> @@ -78,11 +79,14 @@ void show_fiq_list(struct seq_file *p, int prec)
>
> void set_fiq_handler(void *start, unsigned int length)
> {
> -#if defined(CONFIG_CPU_USE_DOMAINS)
> - memcpy((void *)0xffff001c, start, length);
> -#else
> - memcpy(vectors_page + 0x1c, start, length);
> + unsigned long *addr = (void *)0xffff001c;
> +
> +#ifndef CONFIG_CPU_USE_DOMAINS
> + addr = vectors_page + 0x1c;
> #endif
> + if (!cmpxchg(&got_no_fiq_insn, 0, 1))
> + no_fiq_insn = *addr;
> + memcpy(addr, start, length);
> flush_icache_range(0xffff001c, 0xffff001c + length);
> if (!vectors_high())
> flush_icache_range(0x1c, 0x1c + length);
> @@ -126,8 +130,3 @@ EXPORT_SYMBOL(__set_fiq_regs); /* defined in fiqasm.S */
> EXPORT_SYMBOL(__get_fiq_regs); /* defined in fiqasm.S */
> EXPORT_SYMBOL(claim_fiq);
> EXPORT_SYMBOL(release_fiq);
> -
> -void __init init_FIQ(void)
> -{
> - no_fiq_insn = *(unsigned long *)0xffff001c;

it seems that this is wrong. In this case we have an uninitialized variable and
sequential call claim_fiq and release_fiq could be fatal. FIXME please.

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