Re: [PATCH] system timer: fix crash in <100Hz system timer

[H. Peter Anvin]

Andrew Morton wrote:
> > diff --git a/include/linux/acct.h b/include/linux/acct.h
> > index 302eb72..86b848d 100644
> > --- a/include/linux/acct.h
> > +++ b/include/linux/acct.h
> > @@ -173,7 +173,11 @@ typedef struct acct acct_t;
> >  static inline u32 jiffies_to_AHZ(unsigned long x)
> >  {
> >  #if (TICK_NSEC % (NSEC_PER_SEC / AHZ)) == 0
> > -	return x / (HZ / AHZ);
> > +	#if HZ < AHZ
> > +		return x * (AHZ / HZ);
> > +	#else
> > +		return x / (HZ / AHZ);
> > +	#endif
> >  #else
> >          u64 tmp = (u64)x * TICK_NSEC;
> >          do_div(tmp, (NSEC_PER_SEC / AHZ));
> > diff --git a/kernel/time.c b/kernel/time.c
> > index 09d3c45..23af26f 100644
> > --- a/kernel/time.c
> > +++ b/kernel/time.c
> > @@ -565,7 +565,11 @@ EXPORT_SYMBOL(jiffies_to_timeval);
> >  clock_t jiffies_to_clock_t(long x)
> >  {
> >  #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
> > +	#if HZ < USER_HZ
> > +	return x * (USER_HZ / HZ);
> > +	#else
> >  	return x / (HZ / USER_HZ);
> > +	#endif
> >  #else
> >  	u64 tmp = (u64)x * TICK_NSEC;
> >  	do_div(tmp, (NSEC_PER_SEC / USER_HZ));
> > @@ -598,7 +602,12 @@ EXPORT_SYMBOL(clock_t_to_jiffies);
> >  u64 jiffies_64_to_clock_t(u64 x)
> >  {
> >  #if (TICK_NSEC % (NSEC_PER_SEC / USER_HZ)) == 0
> > -	do_div(x, HZ / USER_HZ);
> > +	#if HZ < USER_HZ
> > +		x *= USER_HZ;
> > +		do_div(x, HZ);
> > +	#else
> > +		do_div(x, HZ / USER_HZ);
> > +	#endif
> >  #else
> >  	/*
> >  	 * There are better ways that don't overflow early,
>
> Alas, I get 100% rejects due to conflicting changes from Peter's
> avoid-overflows-in-kernel-timec.patch.
>
> Peter, did that patch propagate this failure, or might it have happily
> fixed it?

My patch doesn't touch any of these functions, nor touches any code 
within 70 lines of this patch -- the last line touched is line 478 -- 
and doesn't touch linux/acct.h at all, so how could it cause a conflict?

But no, it doesn't fix this particular problem, even if using a similar 
technique might very well be a better way to do this kind of conversion.

	-hpa
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