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authorHeiko Carstens <heiko.carstens@de.ibm.com>2010-09-10 07:47:29 -0400
committerIngo Molnar <mingo@elte.hu>2010-09-10 10:48:40 -0400
commit27c379f7f89a4d558c685b5d89b5ba2fe79ae701 (patch)
tree206a00ef1cddaa7f5307b0394f24858f3be5f493 /kernel/smp.c
parentdf423dc7f2a801b9a45d7c501a8eb5c529455ea1 (diff)
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 <heiko.carstens@de.ibm.com> Acked-by: Peter Zijlstra <a.p.zijlstra@chello.nl> Acked-by: Jens Axboe <jaxboe@fusionio.com> Cc: Venkatesh Pallipadi <venki@google.com> Cc: Suresh Siddha <suresh.b.siddha@intel.com> LKML-Reference: <20100910114729.GB2827@osiris.boeblingen.de.ibm.com> Signed-off-by: Ingo Molnar <mingo@elte.hu>
Diffstat (limited to 'kernel/smp.c')
-rw-r--r--kernel/smp.c17
1 files 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:
365EXPORT_SYMBOL_GPL(smp_call_function_any); 365EXPORT_SYMBOL_GPL(smp_call_function_any);
366 366
367/** 367/**
368 * __smp_call_function_single(): Run a function on another CPU 368 * __smp_call_function_single(): Run a function on a specific CPU
369 * @cpu: The CPU to run on. 369 * @cpu: The CPU to run on.
370 * @data: Pre-allocated and setup data structure 370 * @data: Pre-allocated and setup data structure
371 * @wait: If true, wait until function has completed on specified CPU.
371 * 372 *
372 * Like smp_call_function_single(), but allow caller to pass in a 373 * Like smp_call_function_single(), but allow caller to pass in a
373 * pre-allocated data structure. Useful for embedding @data inside 374 * pre-allocated data structure. Useful for embedding @data inside
@@ -376,8 +377,10 @@ EXPORT_SYMBOL_GPL(smp_call_function_any);
376void __smp_call_function_single(int cpu, struct call_single_data *data, 377void __smp_call_function_single(int cpu, struct call_single_data *data,
377 int wait) 378 int wait)
378{ 379{
379 csd_lock(data); 380 unsigned int this_cpu;
381 unsigned long flags;
380 382
383 this_cpu = get_cpu();
381 /* 384 /*
382 * Can deadlock when called with interrupts disabled. 385 * Can deadlock when called with interrupts disabled.
383 * We allow cpu's that are not yet online though, as no one else can 386 * 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,
387 WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled() 390 WARN_ON_ONCE(cpu_online(smp_processor_id()) && wait && irqs_disabled()
388 && !oops_in_progress); 391 && !oops_in_progress);
389 392
390 generic_exec_single(cpu, data, wait); 393 if (cpu == this_cpu) {
394 local_irq_save(flags);
395 data->func(data->info);
396 local_irq_restore(flags);
397 } else {
398 csd_lock(data);
399 generic_exec_single(cpu, data, wait);
400 }
401 put_cpu();
391} 402}
392 403
393/** 404/**