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

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Message-ID: <678F3D1BB717D949B966B68EAEB446ED0A6B5423@SZXEMA509-MBX.china.huawei.com>
Date:	Mon, 1 Feb 2016 03:51:00 +0000
From:	"Zengtao (B)" <prime.zeng@...ilicon.com>
To:	"Zengtao (B)" <prime.zeng@...ilicon.com>,
	Arnd Bergmann <arnd@...db.de>
CC:	Thomas Gleixner <tglx@...utronix.de>,
	LKML <linux-kernel@...r.kernel.org>,
	Frederic Weisbecker <fweisbec@...il.com>
Subject: RE: [PATCH] cputime: Fix timeval-->cputime conversion

Hi Arnd:
	I have got a new idea about the problem: 
In include/linux/time64.h
#define NSEC_PER_SEC	1000000000L 
I think we should change it to
#define NSEC_PER_SEC	1000000000LL 

My reason is :
1.  when it is used in a multiplication, it will easily get overflow.
2.  when it don't get overflow, the change has no side affect.

Thanks.
Zengtao

> -----Original Message-----
> From: Zengtao (B)
> Sent: Saturday, January 30, 2016 10:31 AM
> To: 'Arnd Bergmann'
> Cc: Thomas Gleixner; LKML; Frederic Weisbecker
> Subject: RE: [PATCH] cputime: Fix timeval-->cputime conversion
> 
> > -----Original Message-----
> > From: Arnd Bergmann [mailto:arnd@...db.de]
> > Sent: Friday, January 29, 2016 4:46 PM
> > To: Zengtao (B)
> > Cc: Thomas Gleixner; LKML; Frederic Weisbecker
> > Subject: Re: [PATCH] cputime: Fix timeval-->cputime conversion
> >
> > On Friday 29 January 2016 03:12:37 Zengtao wrote:
> > > > -----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?
> >
> > Reading that code again, I think it does not affect sys_nanosleep, but
> > it does affect sys_clock_nanosleep(CLOCK_PROCESS_CPUTIME_ID, ...)
> > along with timer_create/timer_settime with CLOCK_PROCESS_CPUTIME_ID.
> >
> Got it, I will fix the timespec_to_cputime and resend the patch later.
> > 	Arnd