From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_PASS autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 80CAEC04AB4 for ; Tue, 14 May 2019 07:02:22 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 4E8BF214D8 for ; Tue, 14 May 2019 07:02:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1726491AbfENHCU (ORCPT ); Tue, 14 May 2019 03:02:20 -0400 Received: from ozlabs.org ([203.11.71.1]:33657 "EHLO ozlabs.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1726148AbfENHCU (ORCPT ); Tue, 14 May 2019 03:02:20 -0400 Received: from authenticated.ozlabs.org (localhost [127.0.0.1]) (using TLSv1.3 with cipher TLS_AES_256_GCM_SHA384 (256/256 bits) key-exchange ECDHE (P-256) server-signature RSA-PSS (4096 bits) server-digest SHA256) (No client certificate requested) by mail.ozlabs.org (Postfix) with ESMTPSA id 4537sh6nsKz9sMr; Tue, 14 May 2019 17:02:16 +1000 (AEST) From: Michael Ellerman To: "Gautham R. Shenoy" , Paul Mackerras , Nicholas Piggin , "Aneesh Kumar K.V" Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org, "Gautham R. Shenoy" Subject: Re: [RESEND PATCH] powerpc/pseries: Fix cpu_hotplug_lock acquisition in resize_hpt In-Reply-To: <1557480294-808-1-git-send-email-ego@linux.vnet.ibm.com> References: <1557480294-808-1-git-send-email-ego@linux.vnet.ibm.com> Date: Tue, 14 May 2019 17:02:16 +1000 Message-ID: <874l5xtt6v.fsf@concordia.ellerman.id.au> MIME-Version: 1.0 Content-Type: text/plain Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org "Gautham R. Shenoy" writes: > From: "Gautham R. Shenoy" > > Subject: Re: [RESEND PATCH] powerpc/pseries: Fix cpu_hotplug_lock acquisition in resize_hpt ps. A "RESEND" implies the patch is unchanged and you're just resending it because it was ignored. In this case it should have just been "PATCH v2", with a note below the "---" saying "v2: Rebased onto powerpc/next ..." cheers > During a memory hotplug operations involving resizing of the HPT, we > invoke a stop_machine() to perform the resizing. In this code path, we > end up recursively taking the cpu_hotplug_lock, first in > memory_hotplug_begin() and then subsequently in stop_machine(). This > causes the system to hang. With lockdep enabled we get the following > error message before the hang. > > swapper/0/1 is trying to acquire lock: > (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: stop_machine+0x2c/0x60 > > but task is already holding lock: > (____ptrval____) (cpu_hotplug_lock.rw_sem){++++}, at: mem_hotplug_begin+0x20/0x50 > > other info that might help us debug this: > Possible unsafe locking scenario: > > CPU0 > ---- > lock(cpu_hotplug_lock.rw_sem); > lock(cpu_hotplug_lock.rw_sem); > > *** DEADLOCK *** > > Fix this issue by > 1) Requiring all the calls to pseries_lpar_resize_hpt() be made > with cpu_hotplug_lock held. > > 2) In pseries_lpar_resize_hpt() invoke stop_machine_cpuslocked() > as a consequence of 1) > > 3) To satisfy 1), in hpt_order_set(), call mmu_hash_ops.resize_hpt() > with cpu_hotplug_lock held. > > Reported-by: Aneesh Kumar K.V > Signed-off-by: Gautham R. Shenoy > --- > > Rebased this one against powerpc/next instead of linux/master. > > arch/powerpc/mm/book3s64/hash_utils.c | 9 ++++++++- > arch/powerpc/platforms/pseries/lpar.c | 8 ++++++-- > 2 files changed, 14 insertions(+), 3 deletions(-) > > diff --git a/arch/powerpc/mm/book3s64/hash_utils.c b/arch/powerpc/mm/book3s64/hash_utils.c > index 919a861..d07fcafd 100644 > --- a/arch/powerpc/mm/book3s64/hash_utils.c > +++ b/arch/powerpc/mm/book3s64/hash_utils.c > @@ -38,6 +38,7 @@ > #include > #include > #include > +#include > > #include > #include > @@ -1928,10 +1929,16 @@ static int hpt_order_get(void *data, u64 *val) > > static int hpt_order_set(void *data, u64 val) > { > + int ret; > + > if (!mmu_hash_ops.resize_hpt) > return -ENODEV; > > - return mmu_hash_ops.resize_hpt(val); > + cpus_read_lock(); > + ret = mmu_hash_ops.resize_hpt(val); > + cpus_read_unlock(); > + > + return ret; > } > > DEFINE_DEBUGFS_ATTRIBUTE(fops_hpt_order, hpt_order_get, hpt_order_set, "%llu\n"); > diff --git a/arch/powerpc/platforms/pseries/lpar.c b/arch/powerpc/platforms/pseries/lpar.c > index 1034ef1..2fc9756 100644 > --- a/arch/powerpc/platforms/pseries/lpar.c > +++ b/arch/powerpc/platforms/pseries/lpar.c > @@ -859,7 +859,10 @@ static int pseries_lpar_resize_hpt_commit(void *data) > return 0; > } > > -/* Must be called in user context */ > +/* > + * Must be called in user context. The caller should hold the > + * cpus_lock. > + */ > static int pseries_lpar_resize_hpt(unsigned long shift) > { > struct hpt_resize_state state = { > @@ -913,7 +916,8 @@ static int pseries_lpar_resize_hpt(unsigned long shift) > > t1 = ktime_get(); > > - rc = stop_machine(pseries_lpar_resize_hpt_commit, &state, NULL); > + rc = stop_machine_cpuslocked(pseries_lpar_resize_hpt_commit, > + &state, NULL); > > t2 = ktime_get(); > > -- > 1.9.4