On Mon, May 12, 2014 at 09:42:44PM +0200, Michael Kerrisk (man-pages) wrote:
> > Hmm,.. maybe. Can we still change this? Again, maybe, there's not really
> > that much userspace that relies on this.
>
> I think the sched_getparam() change is worthwhile (and the patches
> could (should?) be marked for -stable). I suspect there's no user
> space that relies on the current SCHED_DEADLINE behavior, and it's
> worth avoiding the above breakage for sched_getparam(). I'd be
> inclined to leave sched_getscheduler() as is: there's arguments
> either way for how it should behave.
>
> > In any case, the way I read the little there is on getparam() it seems
> > to imply the only case where it does make sense to call it at all is
> > when sched_getscheduler() returns either SCHED_FIFO or SCHED_RR.
>
> (Yes, that's my understanding too.)
Something like so then, it encodes that reading explicitly.
---
Subject: sched: Change sched_getparam() behaviour vs SCHED_DEADLINE
From: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
Date: Mon May 12 22:22:47 CEST 2014
The way we read POSIX one should only call sched_getparam() when
sched_getscheduler() returns either SCHED_FIFO or SCHED_RR.
Given that we currently return sched_param::sched_priority=0 for all
others, extend the same behaviour to SCHED_DEADLINE.
Requested-by: Michael Kerrisk <mtk.manpages@xxxxxxxxx>
Signed-off-by: Peter Zijlstra <peterz@xxxxxxxxxxxxx>
---
kernel/sched/core.c | 9 +++------
1 file changed, 3 insertions(+), 6 deletions(-)
Index: linux-2.6/kernel/sched/core.c
===================================================================
--- linux-2.6.orig/kernel/sched/core.c
+++ linux-2.6/kernel/sched/core.c
@@ -3759,7 +3759,7 @@ SYSCALL_DEFINE1(sched_getscheduler, pid_
*/
SYSCALL_DEFINE2(sched_getparam, pid_t, pid, struct sched_param __user *, param)
{
- struct sched_param lp;
+ struct sched_param lp = { .sched_priority = 0 };
struct task_struct *p;
int retval;
@@ -3776,11 +3776,8 @@ SYSCALL_DEFINE2(sched_getparam, pid_t, p
if (retval)
goto out_unlock;
- if (task_has_dl_policy(p)) {
- retval = -EINVAL;
- goto out_unlock;
- }
- lp.sched_priority = p->rt_priority;
+ if (task_has_rt_policy(p))
+ lp.sched_priority = p->rt_priority;
rcu_read_unlock();
/*
--
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