[PATCH] sched: allow unsetting SCHED_RESET_ON_FORK when new policy is not realtime

Maarten Lankhorst
2012-10-17T21:18:49Z

When implementing SIGXCPU handling for a thread boosted with rtkit to realtime
priority, I noticed that sched_setscheduler(somepid, SCHED_OTHER) would return
-EPERM because the thread was previously SCHED_RR | SCHED_RESET_ON_FORK,
and looking from the code that flag cannot be reset without sufficient rights.

sched_setscheduler(somepid, SCHED_OTHER | SCHED_RESET_ON_FORK) which worked,
and seems to be the only way to remove realtime priority set by rtkit on all
kernels since the patch was introduced.

This patch allows SCHED_RESET_ON_FORK to be removed when the user sets a new
policy on itself without realtime.

Cc: Stable <stable@vger.kernel.org> [v2.6.32+]
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@canonical.com>

diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 2d8927f..4c0712a 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -3757,6 +3757,12 @@ recheck:
if (param->sched_priority > p->rt_priority &&
param->sched_priority > rlim_rtprio)
return -EPERM;
+
+ /* Normal users shall not reset the
+ * sched_reset_on_fork flag
+ */
+ if (p->sched_reset_on_fork && !reset_on_fork)
+ return -EPERM;
}

/*
@@ -3771,10 +3777,6 @@ recheck:
/* can't change other user's priorities */
if (!check_same_owner(p))
return -EPERM;
-
- /* Normal users shall not reset the sched_reset_on_fork flag */
- if (p->sched_reset_on_fork && !reset_on_fork)
- return -EPERM;
}

if (user) {