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[PATCH] Fix RLIMIT_RTPRIO breakage

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RLIMIT_RTPRIO is supposed to grant non privileged users the right to use
SCHED_FIFO/SCHED_RR scheduling policies with priorites bounded by the
RLIMIT_RTPRIO value via sched_setscheduler(). This is usually used by
audio users.

Unfortunately this is broken in 2.6.13rc3 as you can see in the excerpt
from sched_setscheduler below:

        /*
         * Allow unprivileged RT tasks to decrease priority:
         */
        if (!capable(CAP_SYS_NICE)) {
                /* can't change policy */
                if (policy != p->policy)
                        return -EPERM;

After the above unconditional test which causes sched_setscheduler to
fail with no regard to the RLIMIT_RTPRIO value the following check is made:

               /* can't increase priority */
                if (policy != SCHED_NORMAL &&
                    param->sched_priority > p->rt_priority &&
                    param->sched_priority >
                                p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
                        return -EPERM;

Thus I do believe that the RLIMIT_RTPRIO value must be taken into
account for the policy check, especially as the RLIMIT_RTPRIO limit is
of no use without this change.

The attached patch fixes this problem.

Signed-off-by: Andreas Steinmetz <[email protected]>
Acked-by: Ingo Molnar <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
This commit is contained in:
Andreas Steinmetz 2005-07-23 13:42:04 +02:00 • committed by Linus Torvalds
commit 18586e7216
1 changed files with 2 additions and 1 deletions
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3
kernel/sched.c
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@ -3528,7 +3528,8 @@ recheck:
*/
if (!capable(CAP_SYS_NICE)) {
/* can't change policy */
if (policy != p->policy)
if (policy != p->policy &&
!p->signal->rlim[RLIMIT_RTPRIO].rlim_cur)
return -EPERM;
/* can't increase priority */
if (policy != SCHED_NORMAL &&