On 11/20/2014 02:52 AM, David Rientjes wrote: > On Mon, 10 Nov 2014, Andrey Ryabinin wrote: > >> 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 <[email protected]> > > I think this is just fine, I would just prefer that you do the memset()
I'd rather do kmem_cache_alloc_node(irq_desc_cachep, gfp | __GFP_ZERO, node) instead of memset. > explicitly rather than introduce the new slab function for such a > specialized purpose (unless there's other examples in the kernel where > this would be useful). > I've counted 7 places where kmem_cache_alloc_node(..., gfp | __GFP_ZERO, ...); called. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
