Re: [PATCH] poll(2) timeout values

[Peter Staubach <staubach@redhat.com>]

Willy Tarreau wrote:

> On Thu, Nov 10, 2005 at 05:15:56PM +0000, Alan Cox wrote:
>  
>
> > On Iau, 2005-11-10 at 11:31 -0500, Peter Staubach wrote:
> >    
> >
> > > Clearly, the timeout calculations problem can be fixed without changing
> > > the arguments to the sys_poll() routine.  However, it is cleaner to fix
> > > it this way by ensuring the sizes and types of arguments match.
> > >      
> > There really is no need for the kernel API to match the userspace one,
> > many of our others differ between the syscall interface which is most
> > definitely 'exported' in one sense and the POSIX interface which is
> > defined by libc, posix and the LSB etc
> >
> > No argument about the timeout fix.
> >    
>
> I posted a different fix here about a month ago (but I sent it 3 times,
> as it was twice wrong). Andrew was about to merge it in his tree but I
> have not checked yet. It was different in the sense that it used
> msecs_to_jiffies() to do the arithmetic in the best possible way depending
> on the HZ value and the ints size. Most of the time (when 1000 % HZ == 0),
> it will simplify the operations to a single divide by a constant and
> correctly check for integer overflows. Eg, with HZ=250, a simple 2 bits
> right shift will replace a multiply followed by an divide.
>
> I'll check whether 2.6.14-mm1 has it, otherwise I can repost it.

Yes, I remember the conversation.  I hadn't seen the final patch included
anywhere, so I posted this one.

That said, I think that msecs_to_jiffies() can still suffer from overflows
if (HZ % MSECS_PER_SEC) != 0 && (MSECS_PER_SEC % HZ) != 0.  I'd like to
see the rest of your patch to see how this was worked around.

The patch that I posted does not suffer from overflow issues.

   Thanx...

      ps
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