Commit 896bbb25 authored by Steven Rostedt (VMware)'s avatar Steven Rostedt (VMware) Committed by Ingo Molnar

sched/core: Allow __sched_setscheduler() in interrupts when PI is not used

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: 's avatarLaurent Dufour <ldufour@linux.vnet.ibm.com>
Tested-by: 's avatarLaurent Dufour <ldufour@linux.vnet.ibm.com>
Signed-off-by: 's avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
Signed-off-by: 's avatarPeter Zijlstra (Intel) <peterz@infradead.org>
Cc: Andrew Morton <akpm@osdl.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Fixes: dbc7f069 ("sched: Use replace normalize_task() with __sched_setscheduler()")
Link: http://lkml.kernel.org/r/20170308124654.10e598f2@gandalf.local.homeSigned-off-by: 's avatarIngo Molnar <mingo@kernel.org>
parent a776b968
......@@ -4188,8 +4188,8 @@ static int __sched_setscheduler(struct task_struct *p,
int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE | DEQUEUE_NOCLOCK;
struct rq *rq;
/* May grab non-irq protected spin_locks: */
BUG_ON(in_interrupt());
/* The pi code expects interrupts enabled */
BUG_ON(pi && in_interrupt());
recheck:
/* Double check policy once rq lock held: */
if (policy < 0) {
......
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