Peter, I've just been pinged by someone that triggered this bug again. Can you take this patch and it probably should be marked for stable too.
-- Steve On Thu, 9 Mar 2017 10:18:42 -0500 Steven Rostedt <[email protected]> wrote: > From: "Steven Rostedt (VMware)" <[email protected]> > > > 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. > > Link: http://lkml.kernel.org/r/[email protected] > > Reported-by: Laurent Dufour <[email protected]> > Tested-by: Laurent Dufour <[email protected]> > Fixes: dbc7f069b93a ("sched: Use replace normalize_task() with > __sched_setscheduler()") > Cc: Andrew Morton <[email protected]> > Cc: Thomas Gleixner <[email protected]> > Cc: Ingo Molnar <[email protected]> > Cc: Peter Zijlstra <[email protected]> > Cc: [email protected] > Signed-off-by: Steven Rostedt (VMware) <[email protected]> > --- > kernel/sched/core.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/kernel/sched/core.c b/kernel/sched/core.c > index 3b31fc0..7292fa9 100644 > --- a/kernel/sched/core.c > +++ b/kernel/sched/core.c > @@ -4129,8 +4129,8 @@ static int __sched_setscheduler(struct task_struct *p, > int queue_flags = DEQUEUE_SAVE | DEQUEUE_MOVE; > 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) {
