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SubjectRe: [PATCH] i386: Execute stack overflow warning on interrupt stack v2
Andi Kleen wrote:
> i386: Execute stack overflow warning on interrupt stack v2
>
> [Found the problem that caused the warnings on some configs now]
>
> Previously the reporting printk would run on the process stack, which risks
> overflow an already low stack. Instead execute it on the interrupt stack.
> This makes it more likely for the printk to make it actually out.
>
> It adds one not taken test/branch more to the interrupt path when
> stack overflow checking is enabled. We could avoid that by duplicating
> more code, but that seemed not worth it.
>
> Based on an observation by Eric Sandeen.
>
> v2: Fix warnings in some configs

Did this patch get lost? I'd sure like to see it go in, the stack
overflow warning + heavy dump_stack on the original stack makes the
warning do much more harm than good.

Thanks,
-Eric

> Signed-off-by: Andi Kleen <andi@firstfloor.org>
>
> ---
> arch/x86/kernel/irq_32.c | 51 +++++++++++++++++++++++++++++++----------------
> 1 file changed, 34 insertions(+), 17 deletions(-)
>
> Index: linux/arch/x86/kernel/irq_32.c
> ===================================================================
> --- linux.orig/arch/x86/kernel/irq_32.c
> +++ linux/arch/x86/kernel/irq_32.c
> @@ -61,6 +61,26 @@ static union irq_ctx *hardirq_ctx[NR_CPU
> static union irq_ctx *softirq_ctx[NR_CPUS] __read_mostly;
> #endif
>
> +static void stack_overflow(void)
> +{
> + printk("low stack detected by irq handler\n");
> + dump_stack();
> +}
> +
> +static inline void call_on_stack2(void *func, void *stack,
> + unsigned long arg1, unsigned long arg2)
> +{
> + unsigned long bx;
> + asm volatile(
> + " xchgl %%ebx,%%esp \n"
> + " call *%%edi \n"
> + " movl %%ebx,%%esp \n"
> + : "=a" (arg1), "=d" (arg2), "=b" (bx)
> + : "0" (arg1), "1" (arg2), "2" (stack),
> + "D" (func)
> + : "memory", "cc", "ecx");
> +}
> +
> /*
> * do_IRQ handles all normal device IRQ's (the special
> * SMP cross-CPU interrupts have their own specific
> @@ -76,6 +96,7 @@ unsigned int do_IRQ(struct pt_regs *regs
> union irq_ctx *curctx, *irqctx;
> u32 *isp;
> #endif
> + int overflow = 0;
>
> if (unlikely((unsigned)irq >= NR_IRQS)) {
> printk(KERN_EMERG "%s: cannot handle IRQ %d\n",
> @@ -92,11 +113,8 @@ unsigned int do_IRQ(struct pt_regs *regs
>
> __asm__ __volatile__("andl %%esp,%0" :
> "=r" (sp) : "0" (THREAD_SIZE - 1));
> - if (unlikely(sp < (sizeof(struct thread_info) + STACK_WARN))) {
> - printk("do_IRQ: stack overflow: %ld\n",
> - sp - sizeof(struct thread_info));
> - dump_stack();
> - }
> + if (unlikely(sp < (sizeof(struct thread_info) + STACK_WARN)))
> + overflow = 1;
> }
> #endif
>
> @@ -112,8 +130,6 @@ unsigned int do_IRQ(struct pt_regs *regs
> * current stack (which is the irq stack already after all)
> */
> if (curctx != irqctx) {
> - int arg1, arg2, bx;
> -
> /* build the stack frame on the IRQ stack */
> isp = (u32*) ((char*)irqctx + sizeof(*irqctx));
> irqctx->tinfo.task = curctx->tinfo.task;
> @@ -127,18 +143,19 @@ unsigned int do_IRQ(struct pt_regs *regs
> (irqctx->tinfo.preempt_count & ~SOFTIRQ_MASK) |
> (curctx->tinfo.preempt_count & SOFTIRQ_MASK);
>
> - asm volatile(
> - " xchgl %%ebx,%%esp \n"
> - " call *%%edi \n"
> - " movl %%ebx,%%esp \n"
> - : "=a" (arg1), "=d" (arg2), "=b" (bx)
> - : "0" (irq), "1" (desc), "2" (isp),
> - "D" (desc->handle_irq)
> - : "memory", "cc", "ecx"
> - );
> + /* Execute warning on interrupt stack */
> + if (unlikely(overflow))
> + call_on_stack2(stack_overflow, isp, 0, 0);
> +
> + call_on_stack2(desc->handle_irq, isp, irq, (unsigned long)desc);
> } else
> #endif
> + {
> + /* AK: Slightly bogus here */
> + if (overflow)
> + stack_overflow();
> desc->handle_irq(irq, desc);
> + }
>
> irq_exit();
> set_irq_regs(old_regs);
> --
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