| From 896bbb2522587e3b8eb2a0d204d43ccc1042a00d Mon Sep 17 00:00:00 2001 |
| From: "Steven Rostedt (VMware)" <rostedt@goodmis.org> |
| Date: Thu, 9 Mar 2017 10:18:42 -0500 |
| Subject: sched/core: Allow __sched_setscheduler() in interrupts when PI is not used |
| |
| From: Steven Rostedt (VMware) <rostedt@goodmis.org> |
| |
| commit 896bbb2522587e3b8eb2a0d204d43ccc1042a00d upstream. |
| |
| 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: Laurent Dufour <ldufour@linux.vnet.ibm.com> |
| Tested-by: Laurent Dufour <ldufour@linux.vnet.ibm.com> |
| Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> |
| Signed-off-by: Peter 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: dbc7f069b93a ("sched: Use replace normalize_task() with __sched_setscheduler()") |
| Link: http://lkml.kernel.org/r/20170308124654.10e598f2@gandalf.local.home |
| Signed-off-by: Ingo Molnar <mingo@kernel.org> |
| Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org> |
| |
| |
| --- |
| kernel/sched/core.c | 4 ++-- |
| 1 file changed, 2 insertions(+), 2 deletions(-) |
| |
| --- a/kernel/sched/core.c |
| +++ b/kernel/sched/core.c |
| @@ -3822,8 +3822,8 @@ static int __sched_setscheduler(struct t |
| struct rq *rq; |
| int reset_on_fork; |
| |
| - /* 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) { |
