On 1 July 2013 22:51, Thomas Gleixner <t...@linutronix.de> wrote: > On Mon, 1 Jul 2013, James Hogan wrote: > >> The main kick trigger handler iterates a list of kick handlers and calls >> each one. This is done with the kick_handlers_lock spin lock held, but >> this causes a problem on SMP where IPIs are implemented with kicks. A >> reschedule IPI calls scheduler_ipi() which uses irq_enter() and >> irq_exit(). This results in the scheduler being invoked with >> kick_handlers_lock held which can result in a nested kick trigger >> attempting to acquire the lock, resulting in deadlock. >> >> irq_enter() and irq_exit() can nest, so call them from the main kick >> interrupt handler so that softirqs are only handled after >> kick_handlers_lock is released. > > This changelog is confusing. What I decode from the patch is, that you > are adding a missing irq_enter/exit pair to the kick_handler, right ?
Yes. Previously the outermost pair of irq_enter/exit was inside the spin lock critical section (inside scheduler_ipi). so soft-irqs (apparently including the scheduler) would run from irq_exit with the spinlock still held. Now it waits until the new outermost irq_exit(), after the spin lock is released. I should probably have increased the number of lines of diff context. http://lxr.linux.no/#linux+v3.10/arch/metag/kernel/kick.c#L66 Cheers James -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
