From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from Galois.linutronix.de (linutronix.de [IPv6:2001:470:1f0b:db:abcd:42:0:1]) (using TLSv1.2 with cipher DHE-RSA-AES128-SHA (128/128 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id AD8091A01EA for ; Tue, 8 Mar 2016 20:04:05 +1100 (AEDT) Date: Tue, 8 Mar 2016 10:03:56 +0100 From: Sebastian Andrzej Siewior To: Benjamin Herrenschmidt Cc: "Aneesh Kumar K.V" , linuxppc-dev@lists.ozlabs.org, Paul Mackerras , Michael Ellerman , Christoph Lameter , Scott Wood Subject: [PATCH v2] powerpc: mm: fixup preempt undefflow with huge pages Message-ID: <20160308090356.GA21842@linutronix.de> References: <20160307135506.GA12595@linutronix.de> <877fheti8i.fsf@linux.vnet.ibm.com> <1457394104.2943.69.camel@kernel.crashing.org> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 In-Reply-To: <1457394104.2943.69.camel@kernel.crashing.org> List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , hugepd_free() used __get_cpu_var() once. Nothing ensured that the code accessing the variable did not migrate from one CPU to another and soon this was noticed by Tiejun Chen in 94b09d755462 ("powerpc/hugetlb: Replace __get_cpu_var with get_cpu_var"). So we had it fixed. Christoph Lameter was doing his __get_cpu_var() replaces and forgot PowerPC. Then he noticed this and sent his fixed up batch again which got applied as 69111bac42f5 ("powerpc: Replace __get_cpu_var uses"). The careful reader will noticed one little detail: get_cpu_var() got replaced with this_cpu_ptr(). So now we have a put_cpu_var() which does a preempt_enable() and nothing that does preempt_disable() so we underflow the preempt counter. Cc: Benjamin Herrenschmidt Cc: Christoph Lameter Cc: Michael Ellerman Cc: Signed-off-by: Sebastian Andrzej Siewior --- v1=E2=80=A6v2: - use get_cpu_var() instead of get_cpu_ptr() - correct indentation of put_cpu_var() arch/powerpc/mm/hugetlbpage.c | 4 ++-- 1 file changed, 2 insertions(+), 2 deletions(-) diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c index 744e24bcb85c..4a811ca7ac9d 100644 --- a/arch/powerpc/mm/hugetlbpage.c +++ b/arch/powerpc/mm/hugetlbpage.c @@ -414,13 +414,13 @@ static void hugepd_free(struct mmu_gather *tlb, void = *hugepte) { struct hugepd_freelist **batchp; =20 - batchp =3D this_cpu_ptr(&hugepd_freelist_cur); + batchp =3D &get_cpu_var(hugepd_freelist_cur); =20 if (atomic_read(&tlb->mm->mm_users) < 2 || cpumask_equal(mm_cpumask(tlb->mm), cpumask_of(smp_processor_id()))) { kmem_cache_free(hugepte_cache, hugepte); - put_cpu_var(hugepd_freelist_cur); + put_cpu_var(hugepd_freelist_cur); return; } =20 --=20 2.7.0