linux-kernel - Re: [PATCH] cputime: Fix timeval-->cputime conversion

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Date:	Thu, 28 Jan 2016 12:52:12 +0100
From:	Arnd Bergmann <arnd@...db.de>
To:	Thomas Gleixner <tglx@...utronix.de>
Cc:	zengtao <prime.zeng@...wei.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: Re: [PATCH] cputime: Fix timeval-->cputime conversion

On Thursday 28 January 2016 09:22:04 Thomas Gleixner wrote:
> Cc'ing Arnd
> 
> On Thu, 28 Jan 2016, zengtao wrote:
> 
> > The structure:
> > struct timeval {
> >       __kernel_time_t         tv_sec;         /* seconds */
> >       __kernel_suseconds_t    tv_usec;        /* microseconds */
> > };
> > both __kernel_time_t and __kernel_suseconds_t are short than u64
> > when it is 32bit platform, so force u64 conversion here.
> > 
> > Signed-off-by: zengtao <prime.zeng@...wei.com>
> 
> Reviewed-by: Thomas Gleixner <tglx@...utronix.de>

This seems to miss timespec_to_cputime(), which has the same problem,
so only setitimer() is fixed, but not nanosleep() or timer_settime().

There should probably be some explanation in which cases this happens,
my reading is that can only occur on MIPS32 and ARM32 with "Full dynticks
CPU time accounting" enabled, which is required for CONFIG_NO_HZ_FULL,
so we need this backported to any kernel that includes
31c1fc818715 ("ARM: Kconfig: allow full nohz CPU accounting"), i.e.
v3.13 or higher, correct?

	Arnd

> >  include/asm-generic/cputime_nsecs.h | 3 ++-
> >  1 file changed, 2 insertions(+), 1 deletion(-)
> > 
> > diff --git a/include/asm-generic/cputime_nsecs.h b/include/asm-generic/cputime_nsecs.h
> > index 0419485..e2f7ff9 100644
> > --- a/include/asm-generic/cputime_nsecs.h
> > +++ b/include/asm-generic/cputime_nsecs.h
> > @@ -91,7 +91,8 @@ static inline void cputime_to_timespec(const cputime_t ct, struct timespec *val)
> >   */
> >  static inline cputime_t timeval_to_cputime(const struct timeval *val)
> >  {
> > -     u64 ret = val->tv_sec * NSEC_PER_SEC + val->tv_usec * NSEC_PER_USEC;
> > +     u64 ret = (u64)val->tv_sec * NSEC_PER_SEC +
> > +                     val->tv_usec * NSEC_PER_USEC;
> >       return (__force cputime_t) ret;
> >  }
> >  static inline void cputime_to_timeval(const cputime_t ct, struct timeval *val)
> > -- 
> > 1.9.1
> > 
> >