From: "Steven Rostedt (VMware)" <rost...@goodmis.org>
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/20170308124654.10e59...@gandalf.local.home Reported-by: Laurent Dufour <lduf...@linux.vnet.ibm.com> Tested-by: Laurent Dufour <lduf...@linux.vnet.ibm.com> Fixes: dbc7f069b93a ("sched: Use replace normalize_task() with __sched_setscheduler()") Cc: Andrew Morton <a...@osdl.org> Cc: Thomas Gleixner <t...@linutronix.de> Cc: Ingo Molnar <mi...@elte.hu> Cc: Peter Zijlstra <pet...@infradead.org> Cc: sta...@vger.kernel.org Signed-off-by: Steven Rostedt (VMware) <rost...@goodmis.org> --- 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) { -- 2.9.3
