Commit 4f29112e authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware) Committed by Greg Kroah-Hartman
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sched/core: Allow __sched_setscheduler() in interrupts when PI is not used

commit 896bbb25


When priority inheritance was added back in 2.6.18 to sched_setscheduler(), it
added a path to taking an rt-mutex wait_lock, which is not IRQ safe. As PI
is not a common occurrence, lockdep will likely never trigger if
sched_setscheduler was called from interrupt context. A BUG_ON() was added
to trigger if __sched_setscheduler() was ever called from interrupt context
because there was a possibility to take the wait_lock.

Today the wait_lock is irq safe, but the path to taking it in
sched_setscheduler() is the same as the path to taking it from normal
context. The wait_lock is taken with raw_spin_lock_irq() and released with
raw_spin_unlock_irq() which will indiscriminately enable interrupts,
which would be bad in interrupt context.

The problem is that normalize_rt_tasks, which is called by triggering the
sysrq nice-all-RT-tasks was changed to call __sched_setscheduler(), and this
is done from interrupt context!

Now __sched_setscheduler() takes a "pi" parameter that is used to know if
the priority inheritance should be called or not. As the BUG_ON() only cares
about calling the PI code, it should only bug if called from interrupt
context with the "pi" parameter set to true.
Reported-by: default avatarLaurent Dufour <>
Tested-by: default avatarLaurent Dufour <>
Signed-off-by: default avatarSteven Rostedt (VMware) <>
Signed-off-by: default avatarPeter Zijlstra (Intel) <>
Cc: Andrew Morton <>
Cc: Linus Torvalds <>
Cc: Peter Zijlstra <>
Cc: Thomas Gleixner <>
Fixes: dbc7f069 ("sched: Use replace normalize_task() with __sched_setscheduler()")

Signed-off-by: default avatarIngo Molnar <>
Signed-off-by: default avatarGreg Kroah-Hartman <>
parent 522ac523
......@@ -3822,8 +3822,8 @@ static int __sched_setscheduler(struct task_struct *p,
struct rq *rq;
int reset_on_fork;
/* may grab non-irq protected spin_locks */
/* The pi code expects interrupts enabled */
BUG_ON(pi && in_interrupt());
/* double check policy once rq lock held */
if (policy < 0) {
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