I have opposed this patch http://lkml.kernel.org/r/YYj91Mkt4m8ySIWt@xxxxxxxxxxxxxx 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@xxxxxxxxxx> > 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@xxxxxxxxxx > Signed-off-by: Alexey Makhalov <amakhalov@xxxxxxxxxx> > Reviewed-by: David Hildenbrand <david@xxxxxxxxxx> > Cc: David Hildenbrand <david@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxx> > Cc: Oscar Salvador <osalvador@xxxxxxx> > Cc: Dennis Zhou <dennis@xxxxxxxxxx> > Cc: Tejun Heo <tj@xxxxxxxxxx> > Cc: Christoph Lameter <cl@xxxxxxxxx> > Cc: <stable@xxxxxxxxxxxxxxx> > Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > --- > > 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@xxxxxxxxxx are > > mm-fix-panic-in-__alloc_pages.patch -- Michal Hocko SUSE Labs
