From: Andrew Morton Subject: Re: [PATCH 2/3] [POWERPC] Fix kernel stack allocation alignment Date: Fri, 18 Apr 2008 00:06:18 -0700 Message-ID: <20080418000618.0c46c78f.akpm@linux-foundation.org> References: <20080418065727.5FE1CDE247@ozlabs.org> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Return-path: In-Reply-To: <20080418065727.5FE1CDE247-mnsaURCQ41sdnm+yROfE0A@public.gmane.org> Sender: linux-arch-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org List-ID: To: Benjamin Herrenschmidt Cc: Paul Mackerras , linuxppc-dev-mnsaURCQ41sdnm+yROfE0A@public.gmane.org, linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, Linux-Arch On Fri, 18 Apr 2008 16:56:17 +1000 Benjamin Herrenschmidt wrote: > The powerpc kernel stacks need to be naturally aligned, as they > contain the thread info at the bottom, which is obtained by > clearing the low bits of the stack pointer. > > However, when using 64K pages (the stack is smaller than a page), > we use kmalloc to allocate it, which doesn't provide that guarantee. > > It appeared to work so far... until one enables SLUB debugging > which then returns unaligned pointers. Ooops... > > This patch fixes it by using a slab cache with enforced alignment > for those. It replies on my previous patch that adds a > thread_info_cache_init() callback. > > ... > > +void thread_info_cache_init(void) > +{ > + thread_info_cache = kmem_cache_create("thread_info", THREAD_SIZE, > + THREAD_SIZE, 0, NULL); > + BUG_ON(thread_info_cache == NULL); > +} so... the "0" defeats all of SLAB_DEBUG_FREE, SLAB_RED_ZONE, SLAB_POISON and SLAB_STORE_USER, if the comment in slab.h is to be believed. Was that overkill?