The vma->anon_vma of the child process may be NULL because the entire vma does not contain anonymous pages. In this case, a BUG will occur when the copy_present_page() passes a copy of a non-anonymous page of that vma to the page_add_new_anon_rmap() to set up new anonymous rmap.

------------[ cut here ]------------ kernel BUG at mm/rmap.c:1044! Internal error: Oops - BUG: 0 [#1] SMP Modules linked in: CPU: 2 PID: 3617 Comm: test Not tainted 5.10.149 #1 Hardware name: linux,dummy-virt (DT) pstate: 80000005 (Nzcv daif -PAN -UAO -TCO BTYPE=--) pc : __page_set_anon_rmap+0xbc/0xf8 lr : __page_set_anon_rmap+0xbc/0xf8 sp : ffff800014c1b870 x29: ffff800014c1b870 x28: 0000000000000001 x27: 0000000010100073 x26: ffff1d65c517baa8 x25: ffff1d65cab0f000 x24: ffff1d65c416d800 x23: ffff1d65cab5f248 x22: 0000000020000000 x21: 0000000000000001 x20: 0000000000000000 x19: fffffe75970023c0 x18: 0000000000000000 x17: 0000000000000000 x16: 0000000000000000 x15: 0000000000000000 x14: 0000000000000000 x13: 0000000000000000 x12: 0000000000000000 x11: 0000000000000000 x10: 0000000000000000 x9 : ffffc3096d5fb858 x8 : 0000000000000000 x7 : 0000000000000011 x6 : ffff5a5c9089c000 x5 : 0000000000020000 x4 : ffff5a5c9089c000 x3 : ffffc3096d200000 x2 : ffffc3096e8d0000 x1 : ffff1d65ca3da740 x0 : 0000000000000000 Call trace: __page_set_anon_rmap+0xbc/0xf8 page_add_new_anon_rmap+0x1e0/0x390 copy_pte_range+0xd00/0x1248 copy_page_range+0x39c/0x620 dup_mmap+0x2e0/0x5a8 dup_mm+0x78/0x140 copy_process+0x918/0x1a20 kernel_clone+0xac/0x638 __do_sys_clone+0x78/0xb0 __arm64_sys_clone+0x30/0x40 el0_svc_common.constprop.0+0xb0/0x308 do_el0_svc+0x48/0xb8 el0_svc+0x24/0x38 el0_sync_handler+0x160/0x168 el0_sync+0x180/0x1c0 Code: 97f8ff85 f9400294 17ffffeb 97f8ff82 (d4210000) ---[ end trace a972347688dc9bd4 ]--- Kernel panic - not syncing: Oops - BUG: Fatal exception SMP: stopping secondary CPUs Kernel Offset: 0x43095d200000 from 0xffff800010000000 PHYS_OFFSET: 0xffffe29a80000000 CPU features: 0x08200022,61806082 Memory Limit: none ---[ end Kernel panic - not syncing: Oops - BUG: Fatal exception ]---

This problem has been fixed by the commit <fb3d824d1a46> ("mm/rmap: split page_dup_rmap() into page_dup_file_rmap() and page_try_dup_anon_rmap()"), but still exists in the linux-5.10.y branch.

This patch is not applicable to this version because of the large version differences. Therefore, fix it by adding non-anonymous page check in the copy_present_page().

Cc: stable@vger.kernel.org Fixes: 70e806e4e645 ("mm: Do early cow for pinned pages during fork() for ptes") Signed-off-by: Yuanzheng Song songyuanzheng@huawei.com --- v2 - Modified the comment misalignment. --- mm/memory.c | 11 +++++++++++ 1 file changed, 11 insertions(+)

diff --git a/mm/memory.c b/mm/memory.c index cc50fa0f4590..cbc0a163d705 100644 --- a/mm/memory.c +++ b/mm/memory.c @@ -823,6 +823,17 @@ copy_present_page(struct vm_area_struct *dst_vma, struct vm_area_struct *src_vma if (likely(!page_maybe_dma_pinned(page))) return 1;

+ /* + * The vma->anon_vma of the child process may be NULL + * because the entire vma does not contain anonymous pages. + * A BUG will occur when the copy_present_page() passes + * a copy of a non-anonymous page of that vma to the + * page_add_new_anon_rmap() to set up new anonymous rmap. + * Return 1 if the page is not an anonymous page. + */ + if (!PageAnon(page)) + return 1; + new_page = *prealloc; if (!new_page) return -EAGAIN;