From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e36.co.us.ibm.com (e36.co.us.ibm.com [32.97.110.154]) (using TLSv1.2 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 3FDD41A0007 for ; Thu, 10 Mar 2016 06:34:38 +1100 (AEDT) Received: from localhost by e36.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Wed, 9 Mar 2016 12:34:34 -0700 Received: from b03cxnp07029.gho.boulder.ibm.com (b03cxnp07029.gho.boulder.ibm.com [9.17.130.16]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id AAD603E40067 for ; Wed, 9 Mar 2016 12:34:32 -0700 (MST) Received: from d03av04.boulder.ibm.com (d03av04.boulder.ibm.com [9.17.195.170]) by b03cxnp07029.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u29JYW8h16711692 for ; Wed, 9 Mar 2016 12:34:32 -0700 Received: from d03av04.boulder.ibm.com (loopback [127.0.0.1]) by d03av04.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u29JYVS3013726 for ; Wed, 9 Mar 2016 12:34:32 -0700 From: "Aneesh Kumar K.V" To: Sebastian Andrzej Siewior , Benjamin Herrenschmidt Cc: linuxppc-dev@lists.ozlabs.org, Paul Mackerras , Michael Ellerman , Christoph Lameter , Scott Wood Subject: Re: [PATCH v2] powerpc: mm: fixup preempt undefflow with huge pages In-Reply-To: <20160308090356.GA21842@linutronix.de> References: <20160307135506.GA12595@linutronix.de> <877fheti8i.fsf@linux.vnet.ibm.com> <1457394104.2943.69.camel@kernel.crashing.org> <20160308090356.GA21842@linutronix.de> Date: Thu, 10 Mar 2016 01:04:24 +0530 Message-ID: <87bn6n1m4f.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sebastian Andrzej Siewior writes: > [ text/plain ] > 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. > Reviewed-by: Aneesh Kumar K.V > 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, voi= d *hugepte) > { > struct hugepd_freelist **batchp; >=20=20 > - batchp =3D this_cpu_ptr(&hugepd_freelist_cur); > + batchp =3D &get_cpu_var(hugepd_freelist_cur); >=20=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 > --=20 > 2.7.0