The patch titled
Subject: mm: khugepaged: fix call hpage_collapse_scan_file() for anonymous vma
has been added to the -mm mm-hotfixes-unstable branch. Its filename is
mm-khugepaged-fix-call-hpage_collapse_scan_file-for-anonymous-vma.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/mm-khugepaged-fix-call-hpage_collapse_scan_file-for-anonymous-vma.patch
This patch will later appear in the mm-hotfixes-unstable branch at
git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm
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------------------------------------------------------
From: Liu Shixin <liushixin2@xxxxxxxxxx>
Subject: mm: khugepaged: fix call hpage_collapse_scan_file() for anonymous vma
Date: Sat, 11 Jan 2025 11:45:11 +0800
syzkaller reported such a BUG_ON():
------------[ cut here ]------------
kernel BUG at mm/khugepaged.c:1835!
Internal error: Oops - BUG: 00000000f2000800 [#1] SMP
...
CPU: 6 UID: 0 PID: 8009 Comm: syz.15.106 Kdump: loaded Tainted: G W 6.13.0-rc6 #22
Tainted: [W]=WARN
Hardware name: QEMU KVM Virtual Machine, BIOS 0.0.0 02/06/2015
pstate: 00400005 (nzcv daif +PAN -UAO -TCO -DIT -SSBS BTYPE=--)
pc : collapse_file+0xa44/0x1400
lr : collapse_file+0x88/0x1400
sp : ffff80008afe3a60
...
Call trace:
collapse_file+0xa44/0x1400 (P)
hpage_collapse_scan_file+0x278/0x400
madvise_collapse+0x1bc/0x678
madvise_vma_behavior+0x32c/0x448
madvise_walk_vmas.constprop.0+0xbc/0x140
do_madvise.part.0+0xdc/0x2c8
__arm64_sys_madvise+0x68/0x88
invoke_syscall+0x50/0x120
el0_svc_common.constprop.0+0xc8/0xf0
do_el0_svc+0x24/0x38
el0_svc+0x34/0x128
el0t_64_sync_handler+0xc8/0xd0
el0t_64_sync+0x190/0x198
This indicates that the pgoff is unaligned. After analysis, I confirm the
vma is mapped to /dev/zero. Such a vma certainly has vm_file, but it is
set to anonymous by mmap_zero(). So even if it's mmapped by 2m-unaligned,
it can pass the check in thp_vma_allowable_order() as it is an
anonymous-mmap, but then be collapsed as a file-mmap.
It seems the problem has existed for a long time, but actually, since we
have khugepaged_max_ptes_none check before, we will skip collapse it as it
is /dev/zero and so has no present page. But commit d8ea7cc8547c limit
the check for only khugepaged, so the BUG_ON() can be triggered by
madvise_collapse().
Add vma_is_anonymous() check to make such vma be processed by
hpage_collapse_scan_pmd().
Link: https://lkml.kernel.org/r/20250111034511.2223353-1-liushixin2@xxxxxxxxxx
Fixes: d8ea7cc8547c ("mm/khugepaged: add flag to predicate khugepaged-only behavior")
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
Cc: Chengming Zhou <chengming.zhou@xxxxxxxxx>
Cc: Johannes Weiner <hannes@xxxxxxxxxxx>
Cc: Kefeng Wang <wangkefeng.wang@xxxxxxxxxx>
Cc: Mattew Wilcox <willy@xxxxxxxxxxxxx>
Cc: Muchun Song <muchun.song@xxxxxxxxx>
Cc: Nanyong Sun <sunnanyong@xxxxxxxxxx>
Cc: Qi Zheng <zhengqi.arch@xxxxxxxxxxxxx>
Cc: Yang Shi <yang@xxxxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/khugepaged.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
--- a/mm/khugepaged.c~mm-khugepaged-fix-call-hpage_collapse_scan_file-for-anonymous-vma
+++ a/mm/khugepaged.c
@@ -2422,7 +2422,7 @@ skip:
VM_BUG_ON(khugepaged_scan.address < hstart ||
khugepaged_scan.address + HPAGE_PMD_SIZE >
hend);
- if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
+ if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
struct file *file = get_file(vma->vm_file);
pgoff_t pgoff = linear_page_index(vma,
khugepaged_scan.address);
@@ -2768,7 +2768,7 @@ int madvise_collapse(struct vm_area_stru
mmap_assert_locked(mm);
memset(cc->node_load, 0, sizeof(cc->node_load));
nodes_clear(cc->alloc_nmask);
- if (IS_ENABLED(CONFIG_SHMEM) && vma->vm_file) {
+ if (IS_ENABLED(CONFIG_SHMEM) && !vma_is_anonymous(vma)) {
struct file *file = get_file(vma->vm_file);
pgoff_t pgoff = linear_page_index(vma, addr);
_
Patches currently in -mm which might be from liushixin2@xxxxxxxxxx are
mm-khugepaged-fix-call-hpage_collapse_scan_file-for-anonymous-vma.patch
