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[31.46.247.178]) by smtp.gmail.com with ESMTPSA id lh22-20020a170906f8d600b009b94c545678sm1397665ejb.153.2023.10.18.03.42.52 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 18 Oct 2023 03:42:53 -0700 (PDT) Sender: Ingo Molnar Date: Wed, 18 Oct 2023 12:42:50 +0200 From: Ingo Molnar To: Mike Rapoport Cc: x86@kernel.org, Andrew Morton , Andy Lutomirski , Borislav Petkov , Dave Hansen , David Hildenbrand , "H. Peter Anvin" , Ingo Molnar , Michal Hocko , Peter Zijlstra , Qi Zheng , Thomas Gleixner , linux-kernel@vger.kernel.org, linux-mm@kvack.org Subject: [PATCH v2] x86/mm: Drop 4MB restriction on minimal NUMA node memory size Message-ID: References: <20231017062215.171670-1-rppt@kernel.org> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20231017062215.171670-1-rppt@kernel.org> Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Transfer-Encoding: quoted-printable Content-Type: text/plain; charset="utf-8" * Mike Rapoport wrote: > From: "Mike Rapoport (IBM)" >=20 > Qi Zheng reports crashes in a production environment and provides a > simplified example as a reproducer: >=20 > For example, if we use qemu to start a two NUMA node kernel, > one of the nodes has 2M memory (less than NODE_MIN_SIZE), > and the other node has 2G, then we will encounter the > following panic: >=20 > [ 0.149844] BUG: kernel NULL pointer dereference, address: 000000000= 0000000 > [ 0.150783] #PF: supervisor write access in kernel mode > [ 0.151488] #PF: error_code(0x0002) - not-present page > <...> > [ 0.156056] RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 > <...> > [ 0.169781] Call Trace: > [ 0.170159] > [ 0.170448] deactivate_slab+0x187/0x3c0 > [ 0.171031] ? bootstrap+0x1b/0x10e > [ 0.171559] ? preempt_count_sub+0x9/0xa0 > [ 0.172145] ? kmem_cache_alloc+0x12c/0x440 > [ 0.172735] ? bootstrap+0x1b/0x10e > [ 0.173236] bootstrap+0x6b/0x10e > [ 0.173720] kmem_cache_init+0x10a/0x188 > [ 0.174240] start_kernel+0x415/0x6ac > [ 0.174738] secondary_startup_64_no_verify+0xe0/0xeb > [ 0.175417] > [ 0.175713] Modules linked in: > [ 0.176117] CR2: 0000000000000000 >=20 > The crashes happen because of inconsistency between nodemask that has > nodes with less than 4MB as memoryless and the actual memory fed into > core mm. Presumably the core MM got fixed too to not just crash, but provide some=20 sort of warning? > The commit 9391a3f9c7f1 ("[PATCH] x86_64: Clear more state when ignoring > empty node in SRAT parsing") that introduced minimal size of a NUMA node > does not explain why a node size cannot be less than 4MB and what boot > failures this restriction might fix. >=20 > Since then a lot has changed and core mm won't confuse badly about small > node sizes. Core MM won't get confused ... other than by the above weird Qemu topology,=20 to which it responds with a ... NULL pointer dereference? Seems quite close to the literal definition of 'get confused badly' to me,=20 and doesn't give me the warm fuzzy feeling that giving the core MM even=20 *more* weird topologies is super safe ... :-/ > Drop the limitation for the minimal node size. While I agree with dropping the limitation, and I agree that 9391a3f9c7f1=20 should have provided more of a justification, I believe a core MM fix is in=20 order as well, for it to not crash. [ If it's fixed upstream already,=20 please reference the relevant commit ID. ] Also, the changelog spelling & general presentation were quite low quality=20 - I've fixed it up a bit below, please carry this version going forward.=20 Please spell-check your patches before sending out Nth versions of it,=20 maybe maintainers are skipping them for a reason! Thanks, Ingo =3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D=3D> From: "Mike Rapoport (IBM)" Date: Tue, 17 Oct 2023 09:22:15 +0300 Subject: [PATCH] x86/mm: Drop 4MB restriction on minimal NUMA node memory s= ize Qi Zheng reported crashes in a production environment and provided a simplified example as a reproducer: | For example, if we use qemu to start a two NUMA node kernel, | one of the nodes has 2M memory (less than NODE_MIN_SIZE), | and the other node has 2G, then we will encounter the | following panic: | | BUG: kernel NULL pointer dereference, address: 0000000000000000 | <...> | RIP: 0010:_raw_spin_lock_irqsave+0x22/0x40 | <...> | Call Trace: | | deactivate_slab() | bootstrap() | kmem_cache_init() | start_kernel() | secondary_startup_64_no_verify() The crashes happen because of inconsistency between the nodemask that has nodes with less than 4MB as memoryless, and the actual memory fed into the core mm. The commit: 9391a3f9c7f1 ("[PATCH] x86_64: Clear more state when ignoring empty node = in SRAT parsing") ... that introduced minimal size of a NUMA node does not explain why a node size cannot be less than 4MB and what boot failures this restriction might fix. In the 17 years since then a lot has changed and core mm won't get confused about small node sizes. Drop the limitation for the minimal node size. [ mingo: Improved changelog clarity. ] Reported-by: Qi Zheng Signed-off-by: Mike Rapoport (IBM) Not-Yet-Signed-off-by: Ingo Molnar Acked-by: David Hildenbrand Acked-by: Michal Hocko Link: https://lore.kernel.org/all/20230212110305.93670-1-zhengqi.arch@byted= ance.com/ --- arch/x86/include/asm/numa.h | 7 ------- arch/x86/mm/numa.c | 7 ------- 2 files changed, 14 deletions(-) diff --git a/arch/x86/include/asm/numa.h b/arch/x86/include/asm/numa.h index e3bae2b60a0d..ef2844d69173 100644 --- a/arch/x86/include/asm/numa.h +++ b/arch/x86/include/asm/numa.h @@ -12,13 +12,6 @@ =20 #define NR_NODE_MEMBLKS (MAX_NUMNODES*2) =20 -/* - * Too small node sizes may confuse the VM badly. Usually they - * result from BIOS bugs. So dont recognize nodes as standalone - * NUMA entities that have less than this amount of RAM listed: - */ -#define NODE_MIN_SIZE (4*1024*1024) - extern int numa_off; =20 /* diff --git a/arch/x86/mm/numa.c b/arch/x86/mm/numa.c index c01c5506fd4a..aa39d678fe81 100644 --- a/arch/x86/mm/numa.c +++ b/arch/x86/mm/numa.c @@ -602,13 +602,6 @@ static int __init numa_register_memblks(struct numa_me= minfo *mi) if (start >=3D end) continue; =20 - /* - * Don't confuse VM with a node that doesn't have the - * minimum amount of memory: - */ - if (end && (end - start) < NODE_MIN_SIZE) - continue; - alloc_node_data(nid); }