After enabling alignment checks in UBSan I've noticed a lot of reports like this:
UBSan: Undefined behaviour in ../kernel/irq/chip.c:195:14 member access within misaligned address ffff88003e80d6f8 for type 'struct irq_desc' which requires 16 byte alignment struct irq_desc declared with ____cacheline_internodealigned_in_smp attribute. However in some cases it allocated dynamically via kmalloc(). In general case kmalloc() guaranties only sizeof(void *) alignment. We should use a separate slab cache to make struct irq_desc properly aligned on SMP configuration. This also could slightly reduce memory usage on some configurations. E.g. in my setup sizeof(struct irq_desc) == 320. Which means that kmalloc-512 will be used for allocating irg_desc via kmalloc(). In that case using separate slab cache will save us 192 bytes per each irq_desc. Note: UBSan reports says that 'struct irq_desc' requires 16 byte alignment. It's wrong, in my setup it should be 64 bytes. This looks like a gcc bug, but it doesn't change the fact that irq_desc is misaligned. Signed-off-by: Andrey Ryabinin <a.ryabi...@samsung.com> --- kernel/irq/irqdesc.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c index a1782f8..f22cb87 100644 --- a/kernel/irq/irqdesc.c +++ b/kernel/irq/irqdesc.c @@ -23,6 +23,8 @@ */ static struct lock_class_key irq_desc_lock_class; +static struct kmem_cache *irq_desc_cachep; + #if defined(CONFIG_SMP) static void __init init_irq_default_affinity(void) { @@ -137,9 +139,10 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner) struct irq_desc *desc; gfp_t gfp = GFP_KERNEL; - desc = kzalloc_node(sizeof(*desc), gfp, node); + desc = kmem_cache_zalloc_node(irq_desc_cachep, gfp, node); if (!desc) return NULL; + /* allocate based on nr_cpu_ids */ desc->kstat_irqs = alloc_percpu(unsigned int); if (!desc->kstat_irqs) @@ -158,7 +161,7 @@ static struct irq_desc *alloc_desc(int irq, int node, struct module *owner) err_kstat: free_percpu(desc->kstat_irqs); err_desc: - kfree(desc); + kmem_cache_free(irq_desc_cachep, desc); return NULL; } @@ -174,7 +177,7 @@ static void free_desc(unsigned int irq) free_masks(desc); free_percpu(desc->kstat_irqs); - kfree(desc); + kmem_cache_free(irq_desc_cachep, desc); } static int alloc_descs(unsigned int start, unsigned int cnt, int node, @@ -218,6 +221,8 @@ int __init early_irq_init(void) init_irq_default_affinity(); + irq_desc_cachep = KMEM_CACHE(irq_desc, SLAB_PANIC); + /* Let arch update nr_irqs and return the nr of preallocated irqs */ initcnt = arch_probe_nr_irqs(); printk(KERN_INFO "NR_IRQS:%d nr_irqs:%d %d\n", NR_IRQS, nr_irqs, initcnt); -- 2.1.3 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/