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[91.12.104.16]) by smtp.gmail.com with ESMTPSA id g10sm2746870wmq.13.2021.11.02.05.06.07 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Tue, 02 Nov 2021 05:06:07 -0700 (PDT) Message-ID: <42abfba6-b27e-ca8b-8cdf-883a9398b506@redhat.com> Date: Tue, 2 Nov 2021 13:06:06 +0100 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101 Thunderbird/91.2.0 To: Michal Hocko Cc: Alexey Makhalov , "linux-mm@kvack.org" , Andrew Morton , "linux-kernel@vger.kernel.org" , "stable@vger.kernel.org" , Oscar Salvador References: <20211101201312.11589-1-amakhalov@vmware.com> <7136c959-63ff-b866-b8e4-f311e0454492@redhat.com> From: David Hildenbrand Organization: Red Hat Subject: Re: [PATCH] mm: fix panic in __alloc_pages In-Reply-To: X-Mimecast-Spam-Score: 0 X-Mimecast-Originator: redhat.com Content-Language: en-US Content-Type: text/plain; charset=UTF-8 X-Rspamd-Server: rspam04 X-Rspamd-Queue-Id: D289710000AF Authentication-Results: imf12.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=OlSUrgii; spf=none (imf12.hostedemail.com: domain of david@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=david@redhat.com; dmarc=pass (policy=none) header.from=redhat.com X-Stat-Signature: s1yeiqhw4as5p8kwednr1sscot31y5re X-HE-Tag: 1635854773-210040 Content-Transfer-Encoding: quoted-printable X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On 02.11.21 12:44, Michal Hocko wrote: > On Tue 02-11-21 12:00:57, David Hildenbrand wrote: >> On 02.11.21 11:34, Alexey Makhalov wrote: > [...] >>>> The node onlining logic when onlining a CPU sounds bogus as well: Le= t's >>>> take a look at try_offline_node(). It checks that: >>>> 1) That no memory is *present* >>>> 2) That no CPU is *present* >>>> >>>> We should online the node when adding the CPU ("present"), not when >>>> onlining the CPU. >>> >>> Possible. >>> Assuming try_online_node was moved under add_cpu(), let=E2=80=99s >>> take look on this call stack: >>> add_cpu() >>> try_online_node() >>> __try_online_node() >>> hotadd_new_pgdat() >>> At line 1190 we'll have a problem: >>> 1183 pgdat =3D NODE_DATA(nid); >>> 1184 if (!pgdat) { >>> 1185 pgdat =3D arch_alloc_nodedata(nid); >>> 1186 if (!pgdat) >>> 1187 return NULL; >>> 1188 >>> 1189 pgdat->per_cpu_nodestats =3D >>> 1190 alloc_percpu(struct per_cpu_nodestat); >>> 1191 arch_refresh_nodedata(nid, pgdat); >>> >>> alloc_percpu() will go for all possible CPUs and will eventually end = up >>> calling alloc_pages_node() trying to use subject nid for correspondin= g CPU >>> hitting the same state #2 problem as NODE_DATA(nid) is still NULL and= nid >>> is not yet online. >> >> Right, we will end up calling pcpu_alloc_pages()->alloc_pages_node() f= or >> each possible CPU. We use cpu_to_node() to come up with the NID. >=20 > Shouldn't this be numa_mem_id instead? Memory less nodes are odd little Hm, good question. Most probably yes for offline nodes. diff --git a/mm/percpu-vm.c b/mm/percpu-vm.c index 2054c9213c43..c21ff5bb91dc 100644 --- a/mm/percpu-vm.c +++ b/mm/percpu-vm.c @@ -84,15 +84,19 @@ static int pcpu_alloc_pages(struct pcpu_chunk *chunk, gfp_t gfp) { unsigned int cpu, tcpu; - int i; + int i, nid; =20 gfp |=3D __GFP_HIGHMEM; =20 for_each_possible_cpu(cpu) { + nid =3D cpu_to_node(cpu); + + if (nid =3D=3D NUMA_NO_NODE || !node_online(nid)) + nid =3D numa_mem_id(); for (i =3D page_start; i < page_end; i++) { struct page **pagep =3D &pages[pcpu_page_idx(cpu,= i)]; =20 - *pagep =3D alloc_pages_node(cpu_to_node(cpu), gfp= , 0); + *pagep =3D alloc_pages_node(nid, gfp, 0); if (!*pagep) goto err; } > critters crafted into the MM code without wider considerations. From > time to time we are struggling with some fallouts but the primary thing > is that zonelists should be valid for all memory less nodes. Yes, but a zonelist cannot be correct for an offline node, where we might not even have an allocated pgdat yet. No pgdat, no zonelist. So as soon a= s we allocate the pgdat and set the node online (->hotadd_new_pgdat()), the= zone lists have to be correct. And I can spot an build_all_zonelists() i= n hotadd_new_pgdat(). I agree that someone passing an offline NID into an allocator function should be fixed. Maybe __alloc_pages_bulk() and alloc_pages_node() should bail out directl= y (VM_BUG()) in case we're providing an offline node with eventually no/sta= le pgdat as preferred nid. --=20 Thanks, David / dhildenb