[PATCH] sched_setscheduler: fix? policy checks

8dc3e909 · Oleg Nesterov <[email protected]> · 2006-09-29 02:00:50 -07:00

I am not sure this patch is correct: I can't understand what the current
code does, and I don't know what it was supposed to do.

The comment says:

		 * can't change policy, except between SCHED_NORMAL
		 * and SCHED_BATCH:

The code:

		if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) &&
			(policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) &&

But this is equivalent to:

		if ( (is_rt_policy(policy) && has_rt_policy(p)) &&

which means something different.  We can't _decrease_ the current
->rt_priority with such a check (if rlim[RLIMIT_RTPRIO] == 0).

Probably, it was supposed to be:

		if (	!(policy == SCHED_NORMAL && p->policy == SCHED_BATCH)  &&
			!(policy == SCHED_BATCH  && p->policy == SCHED_NORMAL)

this matches the comment, but strange: it doesn't allow to _drop_ the
realtime priority when rlim[RLIMIT_RTPRIO] == 0.

I think the right check would be:

		/* can't set/change rt policy */
		if (is_rt_policy(policy) &&
				policy != p->policy &&
				!rlim_rtprio)
			return -EPERM;

Signed-off-by: Oleg Nesterov <[email protected]>
Cc: Thomas Gleixner <[email protected]>
Cc: Ingo Molnar <[email protected]>
Cc: Steven Rostedt <[email protected]>
Cc: Nick Piggin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>

Commit: 8dc3e9099e01dfdd53f27f329c268eced03dfef6
Parents: 57a6f51c

Changes

1 files changed · +18 −20

File	Status	Add	Del	Content
kernel/sched.c	modified	+18	−20	View file

kernel/sched.c

View file

diff --git a/kernel/sched.c b/kernel/sched.c
index c3c718a..155a33d 100644
--- a/kernel/sched.c
+++ b/kernel/sched.c
@@ -4116,27 +4116,25 @@ recheck:
 	 * Allow unprivileged RT tasks to decrease priority:
 	 */
 	if (!capable(CAP_SYS_NICE)) {
-		unsigned long rlim_rtprio;
-		unsigned long flags;
-
-		if (!lock_task_sighand(p, &flags))
-			return -ESRCH;
-		rlim_rtprio = p->signal->rlim[RLIMIT_RTPRIO].rlim_cur;
-		unlock_task_sighand(p, &flags);
+		if (is_rt_policy(policy)) {
+			unsigned long rlim_rtprio;
+			unsigned long flags;
+
+			if (!lock_task_sighand(p, &flags))
+				return -ESRCH;
+			rlim_rtprio = p->signal->rlim[RLIMIT_RTPRIO].rlim_cur;
+			unlock_task_sighand(p, &flags);
+
+			/* can't set/change the rt policy */
+			if (policy != p->policy && !rlim_rtprio)
+				return -EPERM;
+
+			/* can't increase priority */
+			if (param->sched_priority > p->rt_priority &&
+			    param->sched_priority > rlim_rtprio)
+				return -EPERM;
+		}
 
-		/*
-		 * can't change policy, except between SCHED_NORMAL
-		 * and SCHED_BATCH:
-		 */
-		if (((policy != SCHED_NORMAL && p->policy != SCHED_BATCH) &&
-			(policy != SCHED_BATCH && p->policy != SCHED_NORMAL)) &&
-				!rlim_rtprio)
-			return -EPERM;
-		/* can't increase priority */
-		if (is_rt_policy(policy) &&
-		    param->sched_priority > p->rt_priority &&
-		    param->sched_priority > rlim_rtprio)
-			return -EPERM;
 		/* can't change other user's priorities */
 		if ((current->euid != p->euid) &&
 		    (current->euid != p->uid))