From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from e33.co.us.ibm.com (e33.co.us.ibm.com [32.97.110.151]) (using TLSv1.2 with cipher CAMELLIA256-SHA (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 580BF1A011D for ; Tue, 8 Mar 2016 02:34:19 +1100 (AEDT) Received: from localhost by e33.co.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Mon, 7 Mar 2016 08:34:13 -0700 Received: from b03cxnp08026.gho.boulder.ibm.com (b03cxnp08026.gho.boulder.ibm.com [9.17.130.18]) by d03dlp02.boulder.ibm.com (Postfix) with ESMTP id A0E0E3E40047 for ; Mon, 7 Mar 2016 08:34:11 -0700 (MST) Received: from d03av03.boulder.ibm.com (d03av03.boulder.ibm.com [9.17.195.169]) by b03cxnp08026.gho.boulder.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id u27FYBBD19267700 for ; Mon, 7 Mar 2016 08:34:11 -0700 Received: from d03av03.boulder.ibm.com (localhost [127.0.0.1]) by d03av03.boulder.ibm.com (8.14.4/8.14.4/NCO v10.0 AVout) with ESMTP id u27FYAkk009240 for ; Mon, 7 Mar 2016 08:34:11 -0700 From: "Aneesh Kumar K.V" To: Sebastian Andrzej Siewior , linuxppc-dev@lists.ozlabs.org, Benjamin Herrenschmidt Cc: Paul Mackerras , Michael Ellerman , Christoph Lameter , Tiejun Chen , Scott Wood Subject: Re: [PATCH] powerpc: mm: fixup preempt undefflow with huge pages In-Reply-To: <20160307135506.GA12595@linutronix.de> References: <20160307135506.GA12595@linutronix.de> Date: Mon, 07 Mar 2016 21:04:05 +0530 Message-ID: <877fheti8i.fsf@linux.vnet.ibm.com> MIME-Version: 1.0 Content-Type: text/plain 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. > > Cc: Benjamin Herrenschmidt > Cc: Christoph Lameter > Cc: Michael Ellerman > Cc: Tiejun Chen > Cc: > Signed-off-by: Sebastian Andrzej Siewior > --- > arch/powerpc/mm/hugetlbpage.c | 2 +- > 1 file changed, 1 insertion(+), 1 deletion(-) > > diff --git a/arch/powerpc/mm/hugetlbpage.c b/arch/powerpc/mm/hugetlbpage.c > index 744e24bcb85c..9e8919b39640 100644 > --- a/arch/powerpc/mm/hugetlbpage.c > +++ b/arch/powerpc/mm/hugetlbpage.c > @@ -414,7 +414,7 @@ static void hugepd_free(struct mmu_gather *tlb, void *hugepte) > { > struct hugepd_freelist **batchp; > > - batchp = this_cpu_ptr(&hugepd_freelist_cur); > + batchp = get_cpu_ptr(&hugepd_freelist_cur); > > if (atomic_read(&tlb->mm->mm_users) < 2 || > cpumask_equal(mm_cpumask(tlb->mm), IMHO it would better if we do batchp = get_cpu_var(hugepd_freelist_cpu); so that it match the existing put_cpu_var(hugepd_freelist_cur); While you are there, can you also fix the wrong indentation on line 423 ? -aneesh