lkml.org 
[lkml]   [2008]   [Dec]   [4]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
SubjectRe: [PATCH] Allow times and time system calls to return smallnegative values
Date
From
On Thu, 2008-12-04 at 16:40 +0100, Ingo Molnar wrote:
> * Paul Mackerras <paulus@samba.org> wrote:
>
> > Ingo Molnar writes:
> >
> > > > + force_successful_syscall_return();
> > > > return compat_jiffies_to_clock_t(jiffies);
> > >
> > > just curious: what code does force_successful_syscall_return() actually
> > > run in the powerpc case - those bits are missing from this patch. I
> > > suspect it sets some sort of flag?
> >
> > It sets the TIF_NOERROR thread flag, which is tested in the syscall
> > exit path along with various other thread flags.
> >
> > force_successful_syscall_return() is defined for powerpc in
> > arch/powerpc/include/asm/ptrace.h. It's nothing new, it has existed
> > for ages and is used in a few other places already. It has existing
> > non-null definitions on alpha, ia64, powerpc, and sparc64.
>
> ok, was just curious. To make this code nicer, we could keep the time
> syscalls from returning small negative numbers.
>
> the core issue is probably:
>
> jiffies.h:#define INITIAL_JIFFIES ((unsigned long)(unsigned int) (-300*HZ))
>
> the thing is, we did INITIAL_JIFFIES to find _in kernel_ jiffies
> wraparoudn bugs (hung timers, broken drivers, etc.) - we did not want to
> confuse userspace with it.
>
> So how about adding INITIAL_JIFFIES to the sys_times() return value?

Na, that will just hide the bug for some 497 days(or 49 days on alpha).
In user space on have to use this workaround(and I think some variation
is in glibc already):

static unsigned long quagga_times(void)
{
#if defined(GNU_LINUX)
unsigned long ret;
errno = 0;
ret = times(NULL); /* Linux can handle NULL */
/* Workaround broken syscall impl.
* A bugfix exists for the kernel, hopefully
* it will make it into 2.6.29
*/
if (errno)
ret = (unsigned long) (-errno);
return ret;
#else
struct tms dummy; /* Only return value is used */
return times(&dummy);
#endif
}



\
 
 \ /
  Last update: 2008-12-04 17:17    [from the cache]
©2003-2014 Jasper Spaans. Advertise on this site