[PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[Andreas Steinmetz]

[-- Attachment #1: Type: text/plain, Size: 1376 bytes --]

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. I would appreciate it if the fix
would make it into 2.6.13.
-- 
Andreas Steinmetz                       SPAMmers use robotrap@domdv.de

[-- Attachment #2: 2.6.13rc3-rtprio.patch --]
[-- Type: text/plain, Size: 405 bytes --]

--- linux.orig/kernel/sched.c	2005-07-22 19:45:05.000000000 +0200
+++ linux/kernel/sched.c	2005-07-22 19:45:42.000000000 +0200
@@ -3528,7 +3528,8 @@
 	 */
 	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 &&

Re: [PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[Lee Revell]

On Sat, 2005-07-23 at 13:42 +0200, Andreas Steinmetz wrote:
> 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:

Please provide the Signed-Off-By line.  Also I have cc'ed Matt Mackall,
the original author of the patch.

This should definitely make it in 2.6.13.

Lee

Re: [PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[Andreas Steinmetz]

Lee Revell wrote:
> On Sat, 2005-07-23 at 13:42 +0200, Andreas Steinmetz wrote:
> 
>>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:
> 
> 
> Please provide the Signed-Off-By line.  Also I have cc'ed Matt Mackall,
> the original author of the patch.

Sorry, I do forget this all the time...

Signed-off-by: Andreas Steinmetz <ast@domdv.de>
-- 
Andreas Steinmetz                       SPAMmers use robotrap@domdv.de

Re: [PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[Ingo Molnar]

* Andreas Steinmetz <ast@domdv.de> wrote:

> 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. I would appreciate it if the 
> fix would make it into 2.6.13.

[back from KS/OLS]

indeed. The effect of the bug is that RLIMIT_RTPRIO is completely
non-functional in 2.6.12.

Acked-by: Ingo Molnar <mingo@elte.hu>

	Ingo

Re: [PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[Paolo Ciarrocchi]

2005/7/26, Ingo Molnar <mingo@elte.hu>:
[...]
> [back from KS/OLS]
> 
> indeed. The effect of the bug is that RLIMIT_RTPRIO is completely
> non-functional in 2.6.12.
> 
> Acked-by: Ingo Molnar <mingo@elte.hu>

Ingo, Lee, Andreas,
the patch seems to be quite simple and is a fix for a regression.
Is anybody going to FW it to the stable team ?

-- 
paoloc.blogspot.com
paoloc.mindsay.com

Re: [PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[Ingo Molnar]

* Paolo Ciarrocchi <paolo.ciarrocchi@gmail.com> wrote:

> 2005/7/26, Ingo Molnar <mingo@elte.hu>:
> [...]
> > [back from KS/OLS]
> > 
> > indeed. The effect of the bug is that RLIMIT_RTPRIO is completely
> > non-functional in 2.6.12.
> > 
> > Acked-by: Ingo Molnar <mingo@elte.hu>
> 
> Ingo, Lee, Andreas,
> the patch seems to be quite simple and is a fix for a regression.
> Is anybody going to FW it to the stable team ?

i'd not put it into stable just yet - the fact that it has not been 
tested in 2.6.12 _at all_ up until very recently means there's little QA 
feedback. Yes, it's simple, but it also triggers something we never did 
before. 2.6.13 ought to be released soon, that should be good enough.

	Ingo

Re: [PATCH] 2.6.13rc3: RLIMIT_RTPRIO broken

[Lee Revell]

On Tue, 2005-07-26 at 14:06 +0200, Ingo Molnar wrote:
> i'd not put it into stable just yet - the fact that it has not been 
> tested in 2.6.12 _at all_ up until very recently means there's little
> QA feedback. Yes, it's simple, but it also triggers something we never
> did before. 2.6.13 ought to be released soon, that should be good
> enough.

Also, no distro is shipping the updated PAM, glibc, and bash packages
needed to use the new feature yet, even in their development releases.
So there would be very little point in putting this in -stable.

Lee