sparse irq_desc[] array: core kernel and x86 changes

Impact: new feature

Problem on distro kernels: irq_desc[NR_IRQS] takes megabytes of RAM with
NR_CPUS set to large values. The goal is to be able to scale up to much
larger NR_IRQS value without impacting the (important) common case.

To solve this, we generalize irq_desc[NR_IRQS] to an (optional) array of
irq_desc pointers.

When CONFIG_SPARSE_IRQ=y is used, we use kzalloc_node to get irq_desc,
this also makes the IRQ descriptors NUMA-local (to the site that calls
request_irq()).

This gets rid of the irq_cfg[] static array on x86 as well: irq_cfg now
uses desc->chip_data for x86 to store irq_cfg.

Signed-off-by: Yinghai Lu <yinghai@kernel.org>
Signed-off-by: Ingo Molnar <mingo@elte.hu>

6 files changed, 197 insertions, 113 deletions

diff --git a/arch/x86/kernel/io_apic.c b/arch/x86/kernel/io_apic.c
index 9043251210fb..9de17f5c1125 100644
--- a/arch/x86/kernel/io_apic.c
+++ b/arch/x86/kernel/io_apic.c
@@ -108,8 +108,33 @@ static int __init parse_noapic(char *str)
 early_param("noapic", parse_noapic);
 
 struct irq_pin_list;
+
+/*
+ * This is performance-critical, we want to do it O(1)
+ *
+ * the indexing order of this array favors 1:1 mappings
+ * between pins and IRQs.
+ */
+
+struct irq_pin_list {
+        int apic, pin;
+        struct irq_pin_list *next;
+};
+
+static struct irq_pin_list *get_one_free_irq_2_pin(int cpu)
+{
+        struct irq_pin_list *pin;
+        int node;
+
+        node = cpu_to_node(cpu);
+
+        pin = kzalloc_node(sizeof(*pin), GFP_ATOMIC, node);
+        printk(KERN_DEBUG "  alloc irq_2_pin on cpu %d node %d\n", cpu, node);
+
+        return pin;
+}
+
 struct irq_cfg {
-        unsigned int irq;
         struct irq_pin_list *irq_2_pin;
         cpumask_t domain;
         cpumask_t old_domain;
@@ -119,83 +144,93 @@ struct irq_cfg {
 };
 
 /* irq_cfg is indexed by the sum of all RTEs in all I/O APICs. */
+#ifdef CONFIG_SPARSE_IRQ
+static struct irq_cfg irq_cfgx[] = {
+#else
 static struct irq_cfg irq_cfgx[NR_IRQS] = {
-        [0]  = { .irq =  0, .domain = CPU_MASK_ALL, .vector = IRQ0_VECTOR,  },
-        [1]  = { .irq =  1, .domain = CPU_MASK_ALL, .vector = IRQ1_VECTOR,  },
-        [2]  = { .irq =  2, .domain = CPU_MASK_ALL, .vector = IRQ2_VECTOR,  },
-        [3]  = { .irq =  3, .domain = CPU_MASK_ALL, .vector = IRQ3_VECTOR,  },
-        [4]  = { .irq =  4, .domain = CPU_MASK_ALL, .vector = IRQ4_VECTOR,  },
-        [5]  = { .irq =  5, .domain = CPU_MASK_ALL, .vector = IRQ5_VECTOR,  },
-        [6]  = { .irq =  6, .domain = CPU_MASK_ALL, .vector = IRQ6_VECTOR,  },
-        [7]  = { .irq =  7, .domain = CPU_MASK_ALL, .vector = IRQ7_VECTOR,  },
-        [8]  = { .irq =  8, .domain = CPU_MASK_ALL, .vector = IRQ8_VECTOR,  },
-        [9]  = { .irq =  9, .domain = CPU_MASK_ALL, .vector = IRQ9_VECTOR,  },
-        [10] = { .irq = 10, .domain = CPU_MASK_ALL, .vector = IRQ10_VECTOR, },
-        [11] = { .irq = 11, .domain = CPU_MASK_ALL, .vector = IRQ11_VECTOR, },
-        [12] = { .irq = 12, .domain = CPU_MASK_ALL, .vector = IRQ12_VECTOR, },
-        [13] = { .irq = 13, .domain = CPU_MASK_ALL, .vector = IRQ13_VECTOR, },
-        [14] = { .irq = 14, .domain = CPU_MASK_ALL, .vector = IRQ14_VECTOR, },
-        [15] = { .irq = 15, .domain = CPU_MASK_ALL, .vector = IRQ15_VECTOR, },
+#endif
+        [0]  = { .domain = CPU_MASK_ALL, .vector = IRQ0_VECTOR,  },
+        [1]  = { .domain = CPU_MASK_ALL, .vector = IRQ1_VECTOR,  },
+        [2]  = { .domain = CPU_MASK_ALL, .vector = IRQ2_VECTOR,  },
+        [3]  = { .domain = CPU_MASK_ALL, .vector = IRQ3_VECTOR,  },
+        [4]  = { .domain = CPU_MASK_ALL, .vector = IRQ4_VECTOR,  },
+        [5]  = { .domain = CPU_MASK_ALL, .vector = IRQ5_VECTOR,  },
+        [6]  = { .domain = CPU_MASK_ALL, .vector = IRQ6_VECTOR,  },
+        [7]  = { .domain = CPU_MASK_ALL, .vector = IRQ7_VECTOR,  },
+        [8]  = { .domain = CPU_MASK_ALL, .vector = IRQ8_VECTOR,  },
+        [9]  = { .domain = CPU_MASK_ALL, .vector = IRQ9_VECTOR,  },
+        [10] = { .domain = CPU_MASK_ALL, .vector = IRQ10_VECTOR, },
+        [11] = { .domain = CPU_MASK_ALL, .vector = IRQ11_VECTOR, },
+        [12] = { .domain = CPU_MASK_ALL, .vector = IRQ12_VECTOR, },
+        [13] = { .domain = CPU_MASK_ALL, .vector = IRQ13_VECTOR, },
+        [14] = { .domain = CPU_MASK_ALL, .vector = IRQ14_VECTOR, },
+        [15] = { .domain = CPU_MASK_ALL, .vector = IRQ15_VECTOR, },
 };
 
-#define for_each_irq_cfg(irq, cfg)              \
-        for (irq = 0, cfg = irq_cfgx; irq < nr_irqs; irq++, cfg++)
-
-static struct irq_cfg *irq_cfg(unsigned int irq)
+void __init arch_early_irq_init(void)
 {
-        return irq < nr_irqs ? irq_cfgx + irq : NULL;
-}
+        struct irq_cfg *cfg;
+        struct irq_desc *desc;
+        int count;
+        int i;
 
-static struct irq_cfg *irq_cfg_alloc(unsigned int irq)
-{
-        return irq_cfg(irq);
-}
+        cfg = irq_cfgx;
+        count = ARRAY_SIZE(irq_cfgx);
 
-/*
- * Rough estimation of how many shared IRQs there are, can be changed
- * anytime.
- */
-#define MAX_PLUS_SHARED_IRQS NR_IRQS
-#define PIN_MAP_SIZE (MAX_PLUS_SHARED_IRQS + NR_IRQS)
+        for (i = 0; i < count; i++) {
+                desc = irq_to_desc(i);
+                desc->chip_data = &cfg[i];
+        }
+}
 
-/*
- * This is performance-critical, we want to do it O(1)
- *
- * the indexing order of this array favors 1:1 mappings
- * between pins and IRQs.
- */
+#ifdef CONFIG_SPARSE_IRQ
+static struct irq_cfg *irq_cfg(unsigned int irq)
+{
+        struct irq_cfg *cfg = NULL;
+        struct irq_desc *desc;
 
-struct irq_pin_list {
-        int apic, pin;
-        struct irq_pin_list *next;
-};
+        desc = irq_to_desc(irq);
+        if (desc)
+                cfg = desc->chip_data;
 
-static struct irq_pin_list irq_2_pin_head[PIN_MAP_SIZE];
-static struct irq_pin_list *irq_2_pin_ptr;
+        return cfg;
+}
 
-static void __init irq_2_pin_init(void)
+static struct irq_cfg *get_one_free_irq_cfg(int cpu)
 {
-        struct irq_pin_list *pin = irq_2_pin_head;
-        int i;
+        struct irq_cfg *cfg;
+        int node;
+
+        node = cpu_to_node(cpu);
 
-        for (i = 1; i < PIN_MAP_SIZE; i++)
-                pin[i-1].next = &pin[i];
+        cfg = kzalloc_node(sizeof(*cfg), GFP_ATOMIC, node);
+        printk(KERN_DEBUG "  alloc irq_cfg on cpu %d node %d\n", cpu, node);
 
-        irq_2_pin_ptr = &pin[0];
+        return cfg;
 }
 
-static struct irq_pin_list *get_one_free_irq_2_pin(void)
+void arch_init_chip_data(struct irq_desc *desc, int cpu)
 {
-        struct irq_pin_list *pin = irq_2_pin_ptr;
+        struct irq_cfg *cfg;
 
-        if (!pin)
-                panic("can not get more irq_2_pin\n");
+        cfg = desc->chip_data;
+        if (!cfg) {
+                desc->chip_data = get_one_free_irq_cfg(cpu);
+                if (!desc->chip_data) {
+                        printk(KERN_ERR "can not alloc irq_cfg\n");
+                        BUG_ON(1);
+                }
+        }
+}
 
-        irq_2_pin_ptr = pin->next;
-        pin->next = NULL;
-        return pin;
+#else
+static struct irq_cfg *irq_cfg(unsigned int irq)
+{
+        return irq < nr_irqs ? irq_cfgx + irq : NULL;
 }
 
+#endif
+
 struct io_apic {
         unsigned int index;
         unsigned int unused[3];
@@ -397,16 +432,19 @@ static void set_ioapic_affinity_irq(unsigned int irq, cpumask_t mask)
  * shared ISA-space IRQs, so we have to support them. We are super
  * fast in the common case, and fast for shared ISA-space IRQs.
  */
-static void add_pin_to_irq(unsigned int irq, int apic, int pin)
+static void add_pin_to_irq_cpu(unsigned int irq, int cpu, int apic, int pin)
 {
-        struct irq_cfg *cfg;
         struct irq_pin_list *entry;
+        struct irq_cfg *cfg = irq_cfg(irq);
 
-        /* first time to refer irq_cfg, so with new */
-        cfg = irq_cfg_alloc(irq);
         entry = cfg->irq_2_pin;
         if (!entry) {
-                entry = get_one_free_irq_2_pin();
+                entry = get_one_free_irq_2_pin(cpu);
+                if (!entry) {
+                        printk(KERN_ERR "can not alloc irq_2_pin to add %d - %d\n",
+                                        apic, pin);
+                        return;
+                }
                 cfg->irq_2_pin = entry;
                 entry->apic = apic;
                 entry->pin = pin;
@@ -421,7 +459,7 @@ static void add_pin_to_irq(unsigned int irq, int apic, int pin)
                 entry = entry->next;
         }
 
-        entry->next = get_one_free_irq_2_pin();
+        entry->next = get_one_free_irq_2_pin(cpu);
         entry = entry->next;
         entry->apic = apic;
         entry->pin = pin;
@@ -430,7 +468,7 @@ static void add_pin_to_irq(unsigned int irq, int apic, int pin)
 /*
  * Reroute an IRQ to a different pin.
  */
-static void __init replace_pin_at_irq(unsigned int irq,
+static void __init replace_pin_at_irq(unsigned int irq, int cpu,
                                       int oldapic, int oldpin,
                                       int newapic, int newpin)
 {
@@ -451,7 +489,7 @@ static void __init replace_pin_at_irq(unsigned int irq,
 
         /* why? call replace before add? */
         if (!replaced)
-                add_pin_to_irq(irq, newapic, newpin);
+                add_pin_to_irq_cpu(irq, cpu, newapic, newpin);
 }
 
 static inline void io_apic_modify_irq(unsigned int irq,
@@ -1162,9 +1200,13 @@ void __setup_vector_irq(int cpu)
         /* This function must be called with vector_lock held */
         int irq, vector;
         struct irq_cfg *cfg;
+        struct irq_desc *desc;
 
         /* Mark the inuse vectors */
-        for_each_irq_cfg(irq, cfg) {
+        for_each_irq_desc(irq, desc) {
+                if (!desc)
+                        continue;
+                cfg = desc->chip_data;
                 if (!cpu_isset(cpu, cfg->domain))
                         continue;
                 vector = cfg->vector;
@@ -1356,6 +1398,8 @@ static void __init setup_IO_APIC_irqs(void)
 {
         int apic, pin, idx, irq;
         int notcon = 0;
+        struct irq_desc *desc;
+        int cpu = boot_cpu_id;
 
         apic_printk(APIC_VERBOSE, KERN_DEBUG "init IO_APIC IRQs\n");
 
@@ -1387,7 +1431,12 @@ static void __init setup_IO_APIC_irqs(void)
                         if (multi_timer_check(apic, irq))
                                 continue;
 #endif
-                        add_pin_to_irq(irq, apic, pin);
+                        desc = irq_to_desc_alloc_cpu(irq, cpu);
+                        if (!desc) {
+                                printk(KERN_INFO "can not get irq_desc for %d\n", irq);
+                                continue;
+                        }
+                        add_pin_to_irq_cpu(irq, cpu, apic, pin);
 
                         setup_IO_APIC_irq(apic, pin, irq,
                                         irq_trigger(idx), irq_polarity(idx));
@@ -1448,6 +1497,7 @@ __apicdebuginit(void) print_IO_APIC(void)
         union IO_APIC_reg_03 reg_03;
         unsigned long flags;
         struct irq_cfg *cfg;
+        struct irq_desc *desc;
         unsigned int irq;
 
         if (apic_verbosity == APIC_QUIET)
@@ -1537,8 +1587,13 @@ __apicdebuginit(void) print_IO_APIC(void)
         }
         }
         printk(KERN_DEBUG "IRQ to pin mappings:\n");
-        for_each_irq_cfg(irq, cfg) {
-                struct irq_pin_list *entry = cfg->irq_2_pin;
+        for_each_irq_desc(irq, desc) {
+                struct irq_pin_list *entry;
+
+                if (!desc)
+                        continue;
+                cfg = desc->chip_data;
+                entry = cfg->irq_2_pin;
                 if (!entry)
                         continue;
                 printk(KERN_DEBUG "IRQ%d ", irq);
@@ -2022,6 +2077,7 @@ static unsigned int startup_ioapic_irq(unsigned int irq)
 {
         int was_pending = 0;
         unsigned long flags;
+        struct irq_cfg *cfg;
 
         spin_lock_irqsave(&ioapic_lock, flags);
         if (irq < 16) {
@@ -2029,6 +2085,7 @@ static unsigned int startup_ioapic_irq(unsigned int irq)
                 if (i8259A_irq_pending(irq))
                         was_pending = 1;
         }
+        cfg = irq_cfg(irq);
         __unmask_IO_APIC_irq(irq);
         spin_unlock_irqrestore(&ioapic_lock, flags);
 
@@ -2178,6 +2235,9 @@ static void ir_irq_migration(struct work_struct *work)
         struct irq_desc *desc;
 
         for_each_irq_desc(irq, desc) {
+                if (!desc)
+                        continue;
+
                 if (desc->status & IRQ_MOVE_PENDING) {
                         unsigned long flags;
 
@@ -2229,6 +2289,9 @@ asmlinkage void smp_irq_move_cleanup_interrupt(void)
                 struct irq_cfg *cfg;
                 irq = __get_cpu_var(vector_irq)[vector];
 
+                if (irq == -1)
+                        continue;
+
                 desc = irq_to_desc(irq);
                 if (!desc)
                         continue;
@@ -2430,8 +2493,12 @@ static inline void init_IO_APIC_traps(void)
          * Also, we've got to be careful not to trash gate
          * 0x80, because int 0x80 is hm, kind of importantish. ;)
          */
-        for_each_irq_cfg(irq, cfg) {
-                if (IO_APIC_IRQ(irq) && !cfg->vector) {
+        for_each_irq_desc(irq, desc) {
+                if (!desc)
+                        continue;
+
+                cfg = desc->chip_data;
+                if (IO_APIC_IRQ(irq) && cfg && !cfg->vector) {
                         /*
                          * Hmm.. We don't have an entry for this,
                          * so default to an old-fashioned 8259
@@ -2439,11 +2506,9 @@ static inline void init_IO_APIC_traps(void)
                          */
                         if (irq < 16)
                                 make_8259A_irq(irq);
-                        else {
-                                desc = irq_to_desc(irq);
+                        else
                                 /* Strange. Oh, well.. */
                                 desc->chip = &no_irq_chip;
-                        }
                 }
         }
 }
@@ -2654,7 +2719,7 @@ static inline void __init check_timer(void)
                  * Ok, does IRQ0 through the IOAPIC work?
                  */
                 if (no_pin1) {
-                        add_pin_to_irq(0, apic1, pin1);
+                        add_pin_to_irq_cpu(0, boot_cpu_id, apic1, pin1);
                         setup_timer_IRQ0_pin(apic1, pin1, cfg->vector);
                 }
                 unmask_IO_APIC_irq(0);
@@ -2683,7 +2748,7 @@ static inline void __init check_timer(void)
                 /*
                  * legacy devices should be connected to IO APIC #0
                  */
-                replace_pin_at_irq(0, apic1, pin1, apic2, pin2);
+                replace_pin_at_irq(0, boot_cpu_id, apic1, pin1, apic2, pin2);
                 setup_timer_IRQ0_pin(apic2, pin2, cfg->vector);
                 unmask_IO_APIC_irq(0);
                 enable_8259A_irq(0);
@@ -2902,21 +2967,25 @@ unsigned int create_irq_nr(unsigned int irq_want)
         unsigned int irq;
         unsigned int new;
         unsigned long flags;
-        struct irq_cfg *cfg_new;
-
-        irq_want = nr_irqs - 1;
+        struct irq_cfg *cfg_new = NULL;
+        int cpu = boot_cpu_id;
+        struct irq_desc *desc_new = NULL;
 
         irq = 0;
         spin_lock_irqsave(&vector_lock, flags);
         for (new = irq_want; new > 0; new--) {
                 if (platform_legacy_irq(new))
                         continue;
-                cfg_new = irq_cfg(new);
-                if (cfg_new && cfg_new->vector != 0)
+
+                desc_new = irq_to_desc_alloc_cpu(new, cpu);
+                if (!desc_new) {
+                        printk(KERN_INFO "can not get irq_desc for %d\n", new);
+                        continue;
+                }
+                cfg_new = desc_new->chip_data;
+
+                if (cfg_new->vector != 0)
                         continue;
-                /* check if need to create one */
-                if (!cfg_new)
-                        cfg_new = irq_cfg_alloc(new);
                 if (__assign_irq_vector(new, TARGET_CPUS) == 0)
                         irq = new;
                 break;
@@ -2925,6 +2994,9 @@ unsigned int create_irq_nr(unsigned int irq_want)
 
         if (irq > 0) {
                 dynamic_irq_init(irq);
+                /* restore it, in case dynamic_irq_init clear it */
+                if (desc_new)
+                        desc_new->chip_data = cfg_new;
         }
         return irq;
 }
@@ -2944,8 +3016,16 @@ int create_irq(void)
 void destroy_irq(unsigned int irq)
 {
         unsigned long flags;
+        struct irq_cfg *cfg;
+        struct irq_desc *desc;
 
+        /* store it, in case dynamic_irq_cleanup clear it */
+        desc = irq_to_desc(irq);
+        cfg = desc->chip_data;
         dynamic_irq_cleanup(irq);
+        /* connect back irq_cfg */
+        if (desc)
+                desc->chip_data = cfg;
 
 #ifdef CONFIG_INTR_REMAP
         free_irte(irq);
@@ -3195,26 +3275,13 @@ static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc, int irq)
         return 0;
 }
 
-static unsigned int build_irq_for_pci_dev(struct pci_dev *dev)
-{
-        unsigned int irq;
-
-        irq = dev->bus->number;
-        irq <<= 8;
-        irq |= dev->devfn;
-        irq <<= 12;
-
-        return irq;
-}
-
-int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc)
+int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc)
 {
         unsigned int irq;
         int ret;
         unsigned int irq_want;
 
-        irq_want = build_irq_for_pci_dev(dev) + 0x100;
-
+        irq_want = nr_irqs - 1;
         irq = create_irq_nr(irq_want);
         if (irq == 0)
                 return -1;
@@ -3228,7 +3295,7 @@ int arch_setup_msi_irq(struct pci_dev *dev, struct msi_desc *desc)
                 goto error;
 no_ir:
 #endif
-        ret = setup_msi_irq(dev, desc, irq);
+        ret = setup_msi_irq(dev, msidesc, irq);
         if (ret < 0) {
                 destroy_irq(irq);
                 return ret;
@@ -3246,7 +3313,7 @@ int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
 {
         unsigned int irq;
         int ret, sub_handle;
-        struct msi_desc *desc;
+        struct msi_desc *msidesc;
         unsigned int irq_want;
 
 #ifdef CONFIG_INTR_REMAP
@@ -3254,10 +3321,11 @@ int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
         int index = 0;
 #endif
 
-        irq_want = build_irq_for_pci_dev(dev) + 0x100;
+        irq_want = nr_irqs - 1;
         sub_handle = 0;
-        list_for_each_entry(desc, &dev->msi_list, list) {
-                irq = create_irq_nr(irq_want--);
+        list_for_each_entry(msidesc, &dev->msi_list, list) {
+                irq = create_irq_nr(irq_want);
+                irq_want--;
                 if (irq == 0)
                         return -1;
 #ifdef CONFIG_INTR_REMAP
@@ -3289,7 +3357,7 @@ int arch_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
                 }
 no_ir:
 #endif
-                ret = setup_msi_irq(dev, desc, irq);
+                ret = setup_msi_irq(dev, msidesc, irq);
                 if (ret < 0)
                         goto error;
                 sub_handle++;
@@ -3707,17 +3775,29 @@ int __init io_apic_get_version(int ioapic)
 
 int io_apic_set_pci_routing (int ioapic, int pin, int irq, int triggering, int polarity)
 {
+        struct irq_desc *desc;
+        struct irq_cfg *cfg;
+        int cpu = boot_cpu_id;
+
         if (!IO_APIC_IRQ(irq)) {
                 apic_printk(APIC_QUIET,KERN_ERR "IOAPIC[%d]: Invalid reference to IRQ 0\n",
                         ioapic);
                 return -EINVAL;
         }
 
+        desc = irq_to_desc_alloc_cpu(irq, cpu);
+        if (!desc) {
+                printk(KERN_INFO "can not get irq_desc %d\n", irq);
+                return 0;
+        }
+
         /*
          * IRQs < 16 are already in the irq_2_pin[] map
          */
-        if (irq >= 16)
-                add_pin_to_irq(irq, ioapic, pin);
+        if (irq >= 16) {
+                cfg = desc->chip_data;
+                add_pin_to_irq_cpu(irq, cpu, ioapic, pin);
+        }
 
         setup_IO_APIC_irq(ioapic, pin, irq, triggering, polarity);
 
@@ -3773,7 +3853,8 @@ void __init setup_ioapic_dest(void)
                          * when you have too many devices, because at that time only boot
                          * cpu is online.
                          */
-                        cfg = irq_cfg(irq);
+                        desc = irq_to_desc(irq);
+                        cfg = desc->chip_data;
                         if (!cfg->vector) {
                                 setup_IO_APIC_irq(ioapic, pin, irq,
                                                   irq_trigger(irq_entry),
@@ -3785,7 +3866,6 @@ void __init setup_ioapic_dest(void)
                         /*
                          * Honour affinities which have been set in early boot
                          */
-                        desc = irq_to_desc(irq);
                         if (desc->status &
                             (IRQ_NO_BALANCING | IRQ_AFFINITY_SET))
                                 mask = desc->affinity;
@@ -3846,7 +3926,6 @@ void __init ioapic_init_mappings(void)
         struct resource *ioapic_res;
         int i;
 
-        irq_2_pin_init();
         ioapic_res = ioapic_setup_resources();
         for (i = 0; i < nr_ioapics; i++) {
                 if (smp_found_config) {
diff --git a/arch/x86/kernel/irq.c b/arch/x86/kernel/irq.c
index d1d4dc52f649..3f1d9d18df67 100644
--- a/arch/x86/kernel/irq.c
+++ b/arch/x86/kernel/irq.c
@@ -118,6 +118,9 @@ int show_interrupts(struct seq_file *p, void *v)
         }
 
         desc = irq_to_desc(i);
+        if (!desc)
+                return 0;
+
         spin_lock_irqsave(&desc->lock, flags);
 #ifndef CONFIG_SMP
         any_count = kstat_irqs(i);
diff --git a/arch/x86/kernel/irq_32.c b/arch/x86/kernel/irq_32.c
index a51382672de0..119fc9c8ff7f 100644
--- a/arch/x86/kernel/irq_32.c
+++ b/arch/x86/kernel/irq_32.c
@@ -242,6 +242,8 @@ void fixup_irqs(cpumask_t map)
         for_each_irq_desc(irq, desc) {
                 cpumask_t mask;
 
+                if (!desc)
+                        continue;
                 if (irq == 2)
                         continue;
 
diff --git a/arch/x86/kernel/irq_64.c b/arch/x86/kernel/irq_64.c
index 60eb84eb77a0..900009c70591 100644
--- a/arch/x86/kernel/irq_64.c
+++ b/arch/x86/kernel/irq_64.c
@@ -94,6 +94,8 @@ void fixup_irqs(cpumask_t map)
                 int break_affinity = 0;
                 int set_affinity = 1;
 
+                if (!desc)
+                        continue;
                 if (irq == 2)
                         continue;
 
diff --git a/arch/x86/kernel/irqinit_32.c b/arch/x86/kernel/irqinit_32.c
index 845aa9803e80..5a5651b7f9e6 100644
--- a/arch/x86/kernel/irqinit_32.c
+++ b/arch/x86/kernel/irqinit_32.c
@@ -69,7 +69,6 @@ void __init init_ISA_irqs (void)
          * 16 old-style INTA-cycle interrupts:
          */
         for (i = 0; i < 16; i++) {
-                /* first time call this irq_desc */
                 struct irq_desc *desc = irq_to_desc(i);
 
                 desc->status = IRQ_DISABLED;
diff --git a/arch/x86/kernel/irqinit_64.c b/arch/x86/kernel/irqinit_64.c
index ff0235391285..cd9f42d028d9 100644
--- a/arch/x86/kernel/irqinit_64.c
+++ b/arch/x86/kernel/irqinit_64.c
@@ -143,7 +143,6 @@ void __init init_ISA_irqs(void)
         init_8259A(0);
 
         for (i = 0; i < 16; i++) {
-                /* first time call this irq_desc */
                 struct irq_desc *desc = irq_to_desc(i);
 
                 desc->status = IRQ_DISABLED;