From 27c379f7f89a4d558c685b5d89b5ba2fe79ae701 Mon Sep 17 00:00:00 2001 From: Heiko Carstens Date: Fri, 10 Sep 2010 13:47:29 +0200 Subject: [PATCH 1/2] generic-ipi: Fix deadlock in __smp_call_function_single Just got my 6 way machine to a state where cpu 0 is in an endless loop within __smp_call_function_single. All other cpus are idle. The call trace on cpu 0 looks like this: __smp_call_function_single scheduler_tick update_process_times tick_sched_timer __run_hrtimer hrtimer_interrupt clock_comparator_work do_extint ext_int_handler ----> timer irq cpu_idle __smp_call_function_single() got called from nohz_balancer_kick() (inlined) with the remote cpu being 1, wait being 0 and the per cpu variable remote_sched_softirq_cb (call_single_data) of the current cpu (0). Then it loops forever when it tries to grab the lock of the call_single_data, since it is already locked and enqueued on cpu 0. My theory how this could have happened: for some reason the scheduler decided to call __smp_call_function_single() on it's own cpu, and sends an IPI to itself. The interrupt stays pending since IRQs are disabled. If then the hypervisor schedules the cpu away it might happen that upon rescheduling both the IPI and the timer IRQ are pending. If then interrupts are enabled again it depends which one gets scheduled first. If the timer interrupt gets delivered first we end up with the local deadlock as seen in the calltrace above. Let's make __smp_call_function_single() check if the target cpu is the current cpu and execute the function immediately just like smp_call_function_single does. That should prevent at least the scenario described here. It might also be that the scheduler is not supposed to call __smp_call_function_single with the remote cpu being the current cpu, but that is a different issue. Signed-off-by: Heiko Carstens Acked-by: Peter Zijlstra Acked-by: Jens Axboe Cc: Venkatesh Pallipadi Cc: Suresh Siddha LKML-Reference: <20100910114729.GB2827@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar --- kernel/smp.c | 17 ++++++++++++++--- 1 file changed, 14 insertions(+), 3 deletions(-) diff --git a/kernel/smp.c b/kernel/smp.c index 75c970c715d3..ed6aacfcb7ef 100644 --- a/kernel/smp.c +++ b/kernel/smp.c @@ -365,9 +365,10 @@ call: EXPORT_SYMBOL_GPL(smp_call_function_any); /** - * __smp_call_function_single(): Run a function on another CPU + * __smp_call_function_single(): Run a function on a specific CPU * @cpu: The CPU to run on. * @data: Pre-allocated and setup data structure + * @wait: If true, wait until function has completed on specified CPU. * * Like smp_call_function_single(), but allow caller to pass in a * pre-allocated data structure. Useful for embedding @data inside @@ -376,8 +377,10 @@ EXPORT_SYMBOL_GPL(smp_call_function_any); void __smp_call_function_single(int cpu, struct call_single_data *data, int wait) { - csd_lock(data); + unsigned int this_cpu; + unsigned long flags; + this_cpu = get_cpu(); /* * Can deadlock when called with interrupts disabled. * We allow cpu's that are not yet online though, as no one else can @@ -387,7 +390,15 @@ void __smp_call_function_single(int cpu, struct call_single_data *data, WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled() && !oops_in_progress); - generic_exec_single(cpu, data, wait); + if (cpu == this_cpu) { + local_irq_save(flags); + data->func(data->info); + local_irq_restore(flags); + } else { + csd_lock(data); + generic_exec_single(cpu, data, wait); + } + put_cpu(); } /** From b3a084b9b684622b149e8dcf03855bf0d5fb588b Mon Sep 17 00:00:00 2001 From: Eric Dumazet Date: Wed, 22 Sep 2010 08:38:44 +0200 Subject: [PATCH 2/2] rcu: rcu_read_lock_bh_held(): disabling irqs also disables bh rcu_dereference_bh() doesnt know yet about hard irq being disabled, so lockdep can trigger in netpoll_rx() after commit f0f9deae9e7c4 (netpoll: Disable IRQ around RCU dereference in netpoll_rx) Reported-by: Miles Lane Signed-off-by: Eric Dumazet Tested-by: Miles Lane Signed-off-by: Paul E. McKenney --- include/linux/rcupdate.h | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/include/linux/rcupdate.h b/include/linux/rcupdate.h index 9fbc54a2585d..83af1f8d8b74 100644 --- a/include/linux/rcupdate.h +++ b/include/linux/rcupdate.h @@ -454,7 +454,7 @@ static inline notrace void rcu_read_unlock_sched_notrace(void) * Makes rcu_dereference_check() do the dirty work. */ #define rcu_dereference_bh(p) \ - rcu_dereference_check(p, rcu_read_lock_bh_held()) + rcu_dereference_check(p, rcu_read_lock_bh_held() || irqs_disabled()) /** * rcu_dereference_sched - fetch RCU-protected pointer, checking for RCU-sched