On Wed, Jun 25, 2014 at 07:12:34AM +0200, Peter Zijlstra wrote: > On Tue, Jun 24, 2014 at 02:33:41PM -0600, Stephen Warren wrote: > > On 06/10/2014 09:15 AM, Frederic Weisbecker wrote: > > > irq work currently only supports local callbacks. However its code > > > is mostly ready to run remote callbacks and we have some potential user. > > > > > > The full nohz subsystem currently open codes its own remote irq work > > > on top of the scheduler ipi when it wants a CPU to reevaluate its next > > > tick. However this ad hoc solution bloats the scheduler IPI. > > > > > > Lets just extend the irq work subsystem to support remote queuing on top > > > of the generic SMP IPI to handle this kind of user. This shouldn't add > > > noticeable overhead. > > > > I'm running next-20140624 on an ARM system, and this patch causes CPU > > hot(un)plug to Oops for me; the following fires: > > > > void irq_work_run(void) > > { > > BUG_ON(!in_irq()); > > > > I found that Linus's master (8b8f5d971584 "Merge tag 'compress-3.16-rc3' > > of git://git.kernel.org/pub/scm/linux/kernel/git/gregkh/driver-core") > > works fine. I found that this commit inside the tip(?) tree works fine > > (478850160636 "irq_work: Implement remote queueing"). However, if I > > merge the two together, I hit that BUG_ON. > > > > I think the issue is: > > > > This commit adds a call from > > generic_smp_call_function_single_interrupt() to irq_work_run(). > > > > Srivatsa's patch adds a call from hotplug_cfd() to > > flush_smp_call_function_queue() to, which I imagine happens in > > non-interrupt context. Note that this patch moves most of the body of > > generic_smp_call_function_single_interrupt() into > > flush_smp_call_function_queue(). > > Right you are.. I think I'll just remove the BUG_ON(), Frederic? Something a little so like: --- Subject: irq_work: Remove BUG_ON in irq_work_run_list() From: Peter Zijlstra Date: Wed Jun 25 07:13:07 CEST 2014 Because of a collision with 8d056c48e486 ("CPU hotplug, smp: flush any pending IPI callbacks before CPU offline"), which ends up calling hotplug_cfd()->flush_smp_call_function_queue()->run_irq_work(), which is not from IRQ context. Cc: Frederic Weisbecker Reported-by: Stephen Warren Signed-off-by: Peter Zijlstra --- kernel/irq_work.c | 2 -- 1 file changed, 2 deletions(-) --- a/kernel/irq_work.c +++ b/kernel/irq_work.c @@ -130,8 +130,6 @@ static void irq_work_run_list(struct lli struct irq_work *work; struct llist_node *llnode; - BUG_ON(!irqs_disabled()); - if (llist_empty(list)) return;