Re: [UPDATE PATCH][Bug 5132] fix sys_poll() large timeout handling

[Nishanth Aravamudan <nacc@us.ibm.com>]

On 09.09.2005 [19:36:21 -0700], Andrew Morton wrote:
> Nishanth Aravamudan <nacc@us.ibm.com> wrote:
> >
> > +	/*
> >  +	 * We compare HZ with 1000 to work out which side of the
> >  +	 * expression needs conversion.  Because we want to avoid
> >  +	 * converting any value to a numerically higher value, which
> >  +	 * could overflow.
> >  +	 */
> >  +#if HZ > 1000
> >  +	overflow = timeout_msecs >= jiffies_to_msecs(MAX_SCHEDULE_TIMEOUT);
> >  +#else
> >  +	overflow = msecs_to_jiffies(timeout_msecs) >= MAX_SCHEDULE_TIMEOUT;
> >  +#endif
> >  +
> >  +	/*
> >  +	 * If we would overflow in the conversion or a negative timeout
> >  +	 * is requested, sleep indefinitely.
> >  +	 */
> >  +	if (overflow || timeout_msecs < 0)
> >  +		timeout_jiffies = MAX_SCHEDULE_TIMEOUT;
> 
> Do we need to test (timeout_msecs < 0) here?  If we make timeout_msecs
> unsigned long then I think `overflow' will always be correct.

Even though poll is explicitly allowed to take negative values, as per
my man-page:

"#include <sys/poll.h>

int poll(struct pollfd *ufds, unsigned int nfds, int timeout);

...

A negative value means infinite timeout."

Would we have a local variable to store timeout_msecs as well? Or do we
want to make a userspace-visible change like this? I don't have a
preference, I just want to make sure I understand.

Thanks,
Nish