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SubjectRe: + mm-fix-panic-in-__alloc_pages.patch added to -mm tree
I have opposed this patch http://lkml.kernel.org/r/YYj91Mkt4m8ySIWt@dhcp22.suse.cz
There was no response to that feedback. I will not go as far as to nack
it explicitly because pcp allocator is not an area I would nack patches
but seriously, this issue needs a deeper look rather than a paper over
patch. I hope we do not want to do a similar thing to all callers of
cpu_to_mem.

On Mon 08-11-21 12:50:31, Andrew Morton wrote:
>
> The patch titled
> Subject: mm: fix panic in __alloc_pages
> has been added to the -mm tree. Its filename is
> mm-fix-panic-in-__alloc_pages.patch
>
> This patch should soon appear at
> https://ozlabs.org/~akpm/mmots/broken-out/mm-fix-panic-in-__alloc_pages.patch
> and later at
> https://ozlabs.org/~akpm/mmotm/broken-out/mm-fix-panic-in-__alloc_pages.patch
>
> Before you just go and hit "reply", please:
> a) Consider who else should be cc'ed
> b) Prefer to cc a suitable mailing list as well
> c) Ideally: find the original patch on the mailing list and do a
> reply-to-all to that, adding suitable additional cc's
>
> *** Remember to use Documentation/process/submit-checklist.rst when testing your code ***
>
> The -mm tree is included into linux-next and is updated
> there every 3-4 working days
>
> ------------------------------------------------------
> From: Alexey Makhalov <amakhalov@vmware.com>
> Subject: mm: fix panic in __alloc_pages
>
> 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 numa_mem_id().
>
> Link: https://lkml.kernel.org/r/20211108202325.20304-1-amakhalov@vmware.com
> Signed-off-by: Alexey Makhalov <amakhalov@vmware.com>
> Reviewed-by: David Hildenbrand <david@redhat.com>
> Cc: David Hildenbrand <david@redhat.com>
> Cc: Michal Hocko <mhocko@suse.com>
> Cc: Oscar Salvador <osalvador@suse.de>
> Cc: Dennis Zhou <dennis@kernel.org>
> Cc: Tejun Heo <tj@kernel.org>
> Cc: Christoph Lameter <cl@linux.com>
> Cc: <stable@vger.kernel.org>
> Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
> ---
>
> mm/percpu-vm.c | 8 ++++++--
> 1 file changed, 6 insertions(+), 2 deletions(-)
>
> --- a/mm/percpu-vm.c~mm-fix-panic-in-__alloc_pages
> +++ a/mm/percpu-vm.c
> @@ -84,15 +84,19 @@ static int pcpu_alloc_pages(struct pcpu_
> gfp_t gfp)
> {
> unsigned int cpu, tcpu;
> - int i;
> + int i, nid;
>
> gfp |= __GFP_HIGHMEM;
>
> for_each_possible_cpu(cpu) {
> + nid = cpu_to_node(cpu);
> + if (nid == NUMA_NO_NODE || !node_online(nid))
> + nid = numa_mem_id();
> +
> for (i = page_start; i < page_end; i++) {
> struct page **pagep = &pages[pcpu_page_idx(cpu, i)];
>
> - *pagep = alloc_pages_node(cpu_to_node(cpu), gfp, 0);
> + *pagep = alloc_pages_node(nid, gfp, 0);
> if (!*pagep)
> goto err;
> }
> _
>
> Patches currently in -mm which might be from amakhalov@vmware.com are
>
> mm-fix-panic-in-__alloc_pages.patch

--
Michal Hocko
SUSE Labs

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