I found a NULL pointer dereference as followed:
BUG: kernel NULL pointer dereference, address: 0000000000000028
#PF: supervisor read access in kernel mode
#PF: error_code(0x0000) - not-present page
PGD 0 P4D 0
Oops: Oops: 0000 [#1] SMP PTI
CPU: 5 UID: 0 PID: 5964 Comm: sh Kdump: loaded Not tainted 6.13.0-dirty #20
Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.13.0-1ubuntu1.
RIP: 0010:has_unmovable_pages+0x184/0x360
...
Call Trace:
<TASK>
set_migratetype_isolate+0xd1/0x180
start_isolate_page_range+0xd2/0x170
alloc_contig_range_noprof+0x101/0x660
alloc_contig_pages_noprof+0x238/0x290
alloc_gigantic_folio.isra.0+0xb6/0x1f0
only_alloc_fresh_hugetlb_folio.isra.0+0xf/0x60
alloc_pool_huge_folio+0x80/0xf0
set_max_huge_pages+0x211/0x490
__nr_hugepages_store_common+0x5f/0xe0
nr_hugepages_store+0x77/0x80
kernfs_fop_write_iter+0x118/0x200
vfs_write+0x23c/0x3f0
ksys_write+0x62/0xe0
do_syscall_64+0x5b/0x170
entry_SYSCALL_64_after_hwframe+0x76/0x7e
As has_unmovable_pages() call folio_hstate() without hugetlb_lock, there
is a race to free the HugeTLB page between PageHuge() and folio_hstate().
There is no need to add hugetlb_lock here as the HugeTLB page can be freed
in lot of places. So it's enough to unfold folio_hstate() and add a check
to avoid NULL pointer dereference for hugepage_migration_supported().
Fixes: 464c7ffbcb16 ("mm/hugetlb: filter out hugetlb pages if HUGEPAGE migration is not supported.")
Signed-off-by: Liu Shixin <liushixin2@xxxxxxxxxx>
---
mm/page_isolation.c | 9 ++++++++-
1 file changed, 8 insertions(+), 1 deletion(-)
diff --git a/mm/page_isolation.c b/mm/page_isolation.c
index 7e04047977cf..2a38f429defb 100644
--- a/mm/page_isolation.c
+++ b/mm/page_isolation.c
@@ -83,7 +83,14 @@ static struct page *has_unmovable_pages(unsigned long start_pfn, unsigned long e
unsigned int skip_pages;
if (PageHuge(page)) {
- if (!hugepage_migration_supported(folio_hstate(folio)))
+ struct hstate *h;
+
+ /*
+ * The huge page may be freed so can not
+ * use folio_hstate() directly.
+ */
+ h = size_to_hstate(folio_size(folio));
+ if (h && !hugepage_migration_supported(h))
return page;
} else if (!folio_test_lru(folio) && !__folio_test_movable(folio)) {
return page;
--
2.34.1
