[PATCH 6.1 017/236] mm/hugetlb: fix missing hugetlb_lock for resv uncharge

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6.1-stable review patch.  If anyone has any objections, please let me know.


From: Peter Xu <peterx@xxxxxxxxxx>

[ Upstream commit b76b46902c2d0395488c8412e1116c2486cdfcb2 ]

There is a recent report on UFFDIO_COPY over hugetlb:


350:	lockdep_assert_held(&hugetlb_lock);

Should be an issue in hugetlb but triggered in an userfault context, where
it goes into the unlikely path where two threads modifying the resv map
together.  Mike has a fix in that path for resv uncharge but it looks like
the locking criteria was overlooked: hugetlb_cgroup_uncharge_folio_rsvd()
will update the cgroup pointer, so it requires to be called with the lock

Link: https://lkml.kernel.org/r/20240417211836.2742593-3-peterx@xxxxxxxxxx
Fixes: 79aa925bf239 ("hugetlb_cgroup: fix reservation accounting")
Signed-off-by: Peter Xu <peterx@xxxxxxxxxx>
Reported-by: syzbot+4b8077a5fccc61c385a1@xxxxxxxxxxxxxxxxxxxxxxxxx
Reviewed-by: Mina Almasry <almasrymina@xxxxxxxxxx>
Cc: David Hildenbrand <david@xxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
 mm/hugetlb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index e720b9ac28337..e9ae0fc81dfbe 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3190,9 +3190,12 @@ struct page *alloc_huge_page(struct vm_area_struct *vma,
 		rsv_adjust = hugepage_subpool_put_pages(spool, 1);
 		hugetlb_acct_memory(h, -rsv_adjust);
-		if (deferred_reserve)
+		if (deferred_reserve) {
+			spin_lock_irq(&hugetlb_lock);
 					pages_per_huge_page(h), folio);
+			spin_unlock_irq(&hugetlb_lock);
+		}
 	return page;

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