Re: divide error in x86 and cputime

[Oleg Nesterov <oleg@redhat.com>]

On 07/07, Li,Rongqing wrote:
>
> [78250815.703847] divide error: 0000 [#1] PREEMPT SMP NOPTI

...

> It caused by a process with many threads running very long,
> and utime+stime overflowed 64bit, then cause the below div
>
> mul_u64_u64_div_u64(0x69f98da9ba980c00, 0xfffd213aabd74626, 0x09e00900);
>
> I see the comments of mul_u64_u64_div_u64() say:
>
> Will generate an #DE when the result doesn't fit u64, could fix with an
> __ex_table[] entry when it becomes an issu
>
> Seem __ex_table[] entry for div does not work ?

Well, the current version doesn't have an __ex_table[] entry for div...

I do not know what can/should we do in this case... Perhaps

	static inline u64 mul_u64_u64_div_u64(u64 a, u64 mul, u64 div)
	{
		int ok = 0;
		u64 q;

		asm ("mulq %3; 1: divq %4; movl $1,%1; 2:\n"
			_ASM_EXTABLE(1b, 2b)
			: "=a" (q), "+r" (ok)
			: "a" (a), "rm" (mul), "rm" (div)
			: "rdx");

		return ok ? q : -1ul;
	}

?

Should return ULLONG_MAX on #DE.

Oleg.