From mboxrd@z Thu Jan 1 00:00:00 1970 From: matthieu.castet@parrot.com (Matthieu CASTET) Date: Wed, 31 Oct 2012 11:01:44 +0100 Subject: [PATCH] slab : allow SLAB_RED_ZONE and SLAB_STORE_USER to work on arm In-Reply-To: References: <1350386231-770-1-git-send-email-matthieu.castet@parrot.com> Message-ID: <5090F708.3010104@parrot.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Pekka Enberg a ?crit : > Hi, > > (Adding more people to CC.) > > On Tue, Oct 16, 2012 at 2:17 PM, Matthieu CASTET > wrote: >> From: Matthieu CASTET >> >> on cortexA8 (omap3) ralign is 64 and __alignof__(unsigned long long) is 8. >> So we always disable debug. >> >> This patch is based on 5c5e3b33b7cb959a401f823707bee006caadd76e, but fix >> case were align < sizeof(unsigned long long). >> >> Signed-off-by: Matthieu Castet >> CC: Russell King >> CC: Pekka Enberg >> --- >> mm/slab.c | 8 +++----- >> 1 file changed, 3 insertions(+), 5 deletions(-) >> >> diff --git a/mm/slab.c b/mm/slab.c >> index c685475..8427901 100644 >> --- a/mm/slab.c >> +++ b/mm/slab.c >> @@ -2462,9 +2462,6 @@ __kmem_cache_create (const char *name, size_t size, size_t align, >> if (ralign < align) { >> ralign = align; >> } >> - /* disable debug if necessary */ >> - if (ralign > __alignof__(unsigned long long)) >> - flags &= ~(SLAB_RED_ZONE | SLAB_STORE_USER); >> /* >> * 4) Store it. >> */ >> @@ -2491,8 +2488,9 @@ __kmem_cache_create (const char *name, size_t size, size_t align, >> */ >> if (flags & SLAB_RED_ZONE) { >> /* add space for red zone words */ >> - cachep->obj_offset += sizeof(unsigned long long); >> - size += 2 * sizeof(unsigned long long); >> + int offset = max(align, sizeof(unsigned long long)); >> + cachep->obj_offset += offset; >> + size += offset + sizeof(unsigned long long); >> } >> if (flags & SLAB_STORE_USER) { >> /* user store requires one word storage behind the end of > > This piece of code tends to break in peculiar ways every time someone > touches it. I could use some more convincing in the changelog this > time it won't... > Ok, is the following changelog is ok ? The current slab code only allow to put redzone( and user store) info if "buffer alignment(ralign) <= __alignof__(unsigned long long)". This was done because we want to keep the buffer aligned for user even after adding redzone@the beginning of the buffer (the user store is stored after user buffer) [1] But instead of disabling this feature when "ralign > __alignof__(unsigned long long)", we can force the alignment by allocating ralign before user buffer. This is done by setting ralign in obj_offset when "ralign > __alignof__(unsigned long long)" and keeping the old behavior when "ralign <= __alignof__(unsigned long long)" (we set sizeof(unsigned long long)). The 5c5e3b33b7cb959a401f823707bee006caadd76e commit wasn't handling "ralign <= __alignof__(unsigned long long)", that's why it broked some configuration. This was tested on omap3 (ralign is 64 and __alignof__(unsigned long long) is 8) [1] /* * memory layout of objects: * 0 : objp * 0 .. cachep->obj_offset - BYTES_PER_WORD - 1: padding. This ensures that * the end of an object is aligned with the end of the real * allocation. Catches writes behind the end of the allocation. * cachep->obj_offset - BYTES_PER_WORD .. cachep->obj_offset - 1: * redzone word. * cachep->obj_offset: The real object. * cachep->buffer_size - 2* BYTES_PER_WORD: redzone word [BYTES_PER_WORD long] * cachep->buffer_size - 1* BYTES_PER_WORD: last caller address * [BYTES_PER_WORD long] */