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SubjectRe: [rfc][patch] Avoid taking global tasklist_lock for single threaded process at getrusage()

On 12/24/05, Christoph Lameter <clameter@engr.sgi.com> wrote:
> Please put the copy_to_user() invocation into sys_getrusage. That is the
> only function that needs to deal with user space issues includding
> the transfer of the contents of struct rusage. Define
> a local rusage in sys_getrusage. Pass that address to the other functions
> and only copy on success to user space.

rusage_both is called at various places in exit.c, all of which are in
turn called from sys_wait4 through do_wait. They pass a user space
rusage struct pointer and expect the results to be copied there.
Similarly, rusage_self and rusage_children are called from sysirix.c
which also seemingly passes a user space pointer to them. Hence, the
copy to user in all three functions.

n.


> copy_to_user occurs repeatedly:
>
> On Fri, 23 Dec 2005, Ravikiran G Thirumalai wrote:
>
>
> > if (unlikely(!p->signal))
> > - return;
> > + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
> >
> > + cputime_to_timeval(utime, &r.ru_utime);
> > + cputime_to_timeval(stime, &r.ru_stime);
> > +
> > + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
> > +}
> > +
> > +
> > + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
> > }
> >
> > + if (unlikely(!p->signal))
> > + return copy_to_user(ru, &r, sizeof(r)) ? -EFAULT : 0;
> > +
>
> But its only needed here:
>
> > asmlinkage long sys_getrusage(int who, struct rusage __user *ru)
> > {
> > - if (who != RUSAGE_SELF && who != RUSAGE_CHILDREN)
> > - return -EINVAL;
> > - return getrusage(current, who, ru);
> > + switch (who) {
> > + case RUSAGE_SELF:
> > + return getrusage_self(ru);
> > + case RUSAGE_CHILDREN:
> > + return getrusage_children(ru);
> > + default:
> > + break;
> > + }
> > + return -EINVAL;
> > }
>
>


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