[PATCH] Fix RLIMIT_RTPRIO breakage

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 <ast@domdv.de>
Acked-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Linus Torvalds <torvalds@osdl.org>

diff --git a/kernel/sched.c b/kernel/sched.c
index 4107db0dc0919767b72b31e8dd88a5580294a578..a5fb654ea59071015e6516392444fcc5d41b1153 100644 (file)
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -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 &&