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Subject[patch 2/4] x86: Plug irq vector hotplug race
Jin debugged a nasty cpu hotplug race which results in leaking a irq
vector on the newly hotplugged cpu.

cpu N cpu M
native_cpu_up device_shutdown
do_boot_cpu free_msi_irqs
start_secondary arch_teardown_msi_irqs
smp_callin default_teardown_msi_irqs
setup_vector_irq arch_teardown_msi_irq
__setup_vector_irq native_teardown_msi_irq
lock(vector_lock) destroy_irq
install vectors
unlock(vector_lock)
lock(vector_lock)
---> __clear_irq_vector
unlock(vector_lock)
lock(vector_lock)
set_cpu_online
unlock(vector_lock)

This leaves the irq vector(s) which are torn down on CPU M stale in
the vector array of CPU N, because CPU M does not see CPU N online
yet. There is a similar issue with concurrent newly setup interrupts.

The alloc/free protection of irq descriptors does not prevent the
above race, because it merily prevents interrupt descriptors from
going away or changing concurrently.

Prevent this by moving the call to setup_vector_irq() into the
vector_lock held region which protects set_cpu_online():

cpu N cpu M
native_cpu_up device_shutdown
do_boot_cpu free_msi_irqs
start_secondary arch_teardown_msi_irqs
smp_callin default_teardown_msi_irqs
lock(vector_lock) arch_teardown_msi_irq
setup_vector_irq()
__setup_vector_irq native_teardown_msi_irq
install vectors destroy_irq
set_cpu_online
unlock(vector_lock)
lock(vector_lock)
__clear_irq_vector
unlock(vector_lock)

So cpu M either sees the cpu N online before clearing the vector or
cpu N installs the vectors after cpu M has cleared it.

Reported-by: xiao jin <jin.xiao@intel.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
---
arch/x86/kernel/apic/vector.c | 10 ++--------
arch/x86/kernel/smpboot.c | 13 +++++--------
2 files changed, 7 insertions(+), 16 deletions(-)

Index: tip/arch/x86/kernel/apic/vector.c
===================================================================
--- tip.orig/arch/x86/kernel/apic/vector.c
+++ tip/arch/x86/kernel/apic/vector.c
@@ -409,12 +409,6 @@ static void __setup_vector_irq(int cpu)
int irq, vector;
struct apic_chip_data *data;

- /*
- * vector_lock will make sure that we don't run into irq vector
- * assignments that might be happening on another cpu in parallel,
- * while we setup our initial vector to irq mappings.
- */
- raw_spin_lock(&vector_lock);
/* Mark the inuse vectors */
for_each_active_irq(irq) {
data = apic_chip_data(irq_get_irq_data(irq));
@@ -436,16 +430,16 @@ static void __setup_vector_irq(int cpu)
if (!cpumask_test_cpu(cpu, data->domain))
per_cpu(vector_irq, cpu)[vector] = VECTOR_UNDEFINED;
}
- raw_spin_unlock(&vector_lock);
}

/*
- * Setup the vector to irq mappings.
+ * Setup the vector to irq mappings. Must be called with vector_lock held.
*/
void setup_vector_irq(int cpu)
{
int irq;

+ lockdep_assert_held(&vector_lock);
/*
* On most of the platforms, legacy PIC delivers the interrupts on the
* boot cpu. But there are certain platforms where PIC interrupts are
Index: tip/arch/x86/kernel/smpboot.c
===================================================================
--- tip.orig/arch/x86/kernel/smpboot.c
+++ tip/arch/x86/kernel/smpboot.c
@@ -171,11 +171,6 @@ static void smp_callin(void)
apic_ap_setup();

/*
- * Need to setup vector mappings before we enable interrupts.
- */
- setup_vector_irq(smp_processor_id());
-
- /*
* Save our processor parameters. Note: this information
* is needed for clock calibration.
*/
@@ -246,11 +241,13 @@ static void notrace start_secondary(void
#endif

/*
- * We need to hold vector_lock so there the set of online cpus
- * does not change while we are assigning vectors to cpus. Holding
- * this lock ensures we don't half assign or remove an irq from a cpu.
+ * Lock vector_lock and initialize the vectors on this cpu
+ * before setting the cpu online. We must set it online with
+ * vector_lock held to prevent a concurrent setup/teardown
+ * from seeing a half valid vector space.
*/
lock_vector_lock();
+ setup_vector_irq(smp_processor_id());
set_cpu_online(smp_processor_id(), true);
unlock_vector_lock();
cpu_set_state_online(smp_processor_id());



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