Re: [PATCH] hugetlb: fix uninitialized subpool pointer
From: Michal Hocko <mhocko@suse.com>
Date: 2021-02-24 09:46:51
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On Tue 23-02-21 13:55:44, Mike Kravetz wrote:
Gerald Schaefer reported a panic on s390 in hugepage_subpool_put_pages() with linux-next 5.12.0-20210222. Call trace: hugepage_subpool_put_pages.part.0+0x2c/0x138 __free_huge_page+0xce/0x310 alloc_pool_huge_page+0x102/0x120 set_max_huge_pages+0x13e/0x350 hugetlb_sysctl_handler_common+0xd8/0x110 hugetlb_sysctl_handler+0x48/0x58 proc_sys_call_handler+0x138/0x238 new_sync_write+0x10e/0x198 vfs_write.part.0+0x12c/0x238 ksys_write+0x68/0xf8 do_syscall+0x82/0xd0 __do_syscall+0xb4/0xc8 system_call+0x72/0x98 This is a result of the change which moved the hugetlb page subpool pointer from page->private to page[1]->private. When new pages are allocated from the buddy allocator, the private field of the head page will be cleared, but the private field of subpages is not modified. Therefore, old values may remain.
Very interesting. I have expected that the page->private would be in a reasonable state when allocated. On the other hand hugetlb doesn't do __GFP_COMP so tail pages are not initialized by the allocator.
Fix by initializing hugetlb page subpool pointer in prep_new_huge_page().
Fixes: f1280272ae4d ("hugetlb: use page.private for hugetlb specific page flags")This is not a stable sha to refer to as it comes from linux next.
Reported-by: Gerald Schaefer <gerald.schaefer@linux.ibm.com> Signed-off-by: Mike Kravetz <redacted>
Acked-by: Michal Hocko <mhocko@suse.com> I think this would be worth a separate patch rather than having it folded into the original patch. Thi is really subtle.
quoted hunk ↗ jump to hunk
--- mm/hugetlb.c | 1 + 1 file changed, 1 insertion(+)diff --git a/mm/hugetlb.c b/mm/hugetlb.c index c232cb67dda2..7ae5c18c98a7 100644 --- a/mm/hugetlb.c +++ b/mm/hugetlb.c@@ -1465,6 +1465,7 @@ static void prep_new_huge_page(struct hstate *h, struct page *page, int nid) { INIT_LIST_HEAD(&page->lru); set_compound_page_dtor(page, HUGETLB_PAGE_DTOR); + hugetlb_set_page_subpool(page, NULL); set_hugetlb_cgroup(page, NULL); set_hugetlb_cgroup_rsvd(page, NULL); spin_lock(&hugetlb_lock);-- 2.29.2
-- Michal Hocko SUSE Labs