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

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Date:	Fri, 29 Jan 2016 03:12:37 +0000
From:	"Zengtao (B)" <prime.zeng@...ilicon.com>
To:	Arnd Bergmann <arnd@...db.de>, Thomas Gleixner <tglx@...utronix.de>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: RE: [PATCH] cputime: Fix timeval-->cputime conversion

> -----Original Message-----
> From: Arnd Bergmann [mailto:arnd@...db.de]
> Sent: Thursday, January 28, 2016 7:52 PM
> To: Thomas Gleixner
> Cc: Zengtao (B); LKML; Frederic Weisbecker
> 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().
Yes, I have checked the code just now, the timespec_to_cputime() has the 
same problem.I found the origin issue through setitimer().And I think the 
timespec_to_cputime() only affects timer_settime(),by which means it affects 
nanosleep? 

> 
> 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?
Yes.
> 
> 	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
> > >
> > >