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Date:   Mon, 8 Nov 2021 11:37:08 +0100
From:   Michal Hocko <mhocko@suse.com>
To:     Alexey Makhalov <amakhalov@vmware.com>
Cc:     linux-mm@kvack.org, Andrew Morton <akpm@linux-foundation.org>,
        David Hildenbrand <david@redhat.com>,
        Oscar Salvador <osalvador@suse.de>,
        Dennis Zhou <dennis@kernel.org>, Tejun Heo <tj@kernel.org>,
        Christoph Lameter <cl@linux.com>, linux-kernel@vger.kernel.org,
        stable@vger.kernel.org
Subject: Re: [PATCH v2] mm: fix panic in __alloc_pages
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References: <86BDA7AC-3E7A-4779-9388-9DF7BA7230AA@vmware.com>
 <20211108063650.19435-1-amakhalov@vmware.com>
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On Sun 07-11-21 22:36:50, Alexey Makhalov wrote:
> There is a kernel panic caused by pcpu_alloc_pages() passing
> offlined and uninitialized node to alloc_pages_node() leading
> to panic by NULL dereferencing uninitialized NODE_DATA(nid).
> 
>  CPU2 has been hot-added
>  BUG: unable to handle page fault for address: 0000000000001608
>  #PF: supervisor read access in kernel mode
>  #PF: error_code(0x0000) - not-present page
>  PGD 0 P4D 0
>  Oops: 0000 [#1] SMP PTI
>  CPU: 0 PID: 1 Comm: systemd Tainted: G            E     5.15.0-rc7+ #11
>  Hardware name: VMware, Inc. VMware7,1/440BX Desktop Reference Platform, BIOS VMW
> 
>  RIP: 0010:__alloc_pages+0x127/0x290
>  Code: 4c 89 f0 5b 41 5c 41 5d 41 5e 41 5f 5d c3 44 89 e0 48 8b 55 b8 c1 e8 0c 83 e0 01 88 45 d0 4c 89 c8 48 85 d2 0f 85 1a 01 00 00 <45> 3b 41 08 0f 82 10 01 00 00 48 89 45 c0 48 8b 00 44 89 e2 81 e2
>  RSP: 0018:ffffc900006f3bc8 EFLAGS: 00010246
>  RAX: 0000000000001600 RBX: 0000000000000000 RCX: 0000000000000000
>  RDX: 0000000000000000 RSI: 0000000000000000 RDI: 0000000000000cc2
>  RBP: ffffc900006f3c18 R08: 0000000000000001 R09: 0000000000001600
>  R10: ffffc900006f3a40 R11: ffff88813c9fffe8 R12: 0000000000000cc2
>  R13: 0000000000000000 R14: 0000000000000001 R15: 0000000000000cc2
>  FS:  00007f27ead70500(0000) GS:ffff88807ce00000(0000) knlGS:0000000000000000
>  CS:  0010 DS: 0000 ES: 0000 CR0: 0000000080050033
>  CR2: 0000000000001608 CR3: 000000000582c003 CR4: 00000000001706b0
>  Call Trace:
>   pcpu_alloc_pages.constprop.0+0xe4/0x1c0
>   pcpu_populate_chunk+0x33/0xb0
>   pcpu_alloc+0x4d3/0x6f0
>   __alloc_percpu_gfp+0xd/0x10
>   alloc_mem_cgroup_per_node_info+0x54/0xb0
>   mem_cgroup_alloc+0xed/0x2f0
>   mem_cgroup_css_alloc+0x33/0x2f0
>   css_create+0x3a/0x1f0
>   cgroup_apply_control_enable+0x12b/0x150
>   cgroup_mkdir+0xdd/0x110
>   kernfs_iop_mkdir+0x4f/0x80
>   vfs_mkdir+0x178/0x230
>   do_mkdirat+0xfd/0x120
>   __x64_sys_mkdir+0x47/0x70
>   ? syscall_exit_to_user_mode+0x21/0x50
>   do_syscall_64+0x43/0x90
>   entry_SYSCALL_64_after_hwframe+0x44/0xae
> 
> Panic can be easily reproduced by disabling udev rule for
> automatic onlining hot added CPU followed by CPU with
> memoryless node (NUMA node with CPU only) hot add.
> 
> Hot adding CPU and memoryless node does not bring the node
> to online state. Memoryless node will be onlined only during
> the onlining its CPU.
> 
> Node can be in one of the following states:
> 1. not present.(nid == NUMA_NO_NODE)
> 2. present, but offline (nid > NUMA_NO_NODE, node_online(nid) == 0,
> 				NODE_DATA(nid) == NULL)
> 3. present and online (nid > NUMA_NO_NODE, node_online(nid) > 0,
> 				NODE_DATA(nid) != NULL)
> 
> Percpu code is doing allocations for all possible CPUs. The
> issue happens when it serves hot added but not yet onlined
> CPU when its node is in 2nd state. This node is not ready
> to use, fallback to node_mem_id().

I do agree that cpu_to_mem usage is better here. But I still think this
is papering over a deeper problem. We should never allow cpu_to_mem to
return an invalid numa node.

-- 
Michal Hocko
SUSE Labs