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From: Peter Xu <peterx@redhat.com>
To: linux-mm@kvack.org,
	linux-kernel@vger.kernel.org
Cc: peterx@redhat.com,
	David Hildenbrand <david@redhat.com>,
	Mina Almasry <almasrymina@google.com>,
	Andrew Morton <akpm@linux-foundation.org>,
	Muchun Song <muchun.song@linux.dev>,
	David Rientjes <rientjes@google.com>,
	syzbot+4b8077a5fccc61c385a1@syzkaller.appspotmail.com,
	linux-stable <stable@vger.kernel.org>
Subject: [PATCH 2/3] mm/hugetlb: Fix missing hugetlb_lock for resv uncharge
Date: Wed, 17 Apr 2024 17:18:35 -0400
Message-ID: <20240417211836.2742593-3-peterx@redhat.com>
In-Reply-To: <20240417211836.2742593-1-peterx@redhat.com>
References: <20240417211836.2742593-1-peterx@redhat.com>
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There is a recent report on UFFDIO_COPY over hugetlb:

https://lore.kernel.org/all/000000000000ee06de0616177560@google.com/

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
held.

Looks like a stable material, so have it copied.

Reported-by: syzbot+4b8077a5fccc61c385a1@syzkaller.appspotmail.com
Cc: Mina Almasry <almasrymina@google.com>
Cc: David Hildenbrand <david@redhat.com>
Cc: linux-stable <stable@vger.kernel.org>
Fixes: 79aa925bf239 ("hugetlb_cgroup: fix reservation accounting")
Signed-off-by: Peter Xu <peterx@redhat.com>
---
 mm/hugetlb.c | 5 ++++-
 1 file changed, 4 insertions(+), 1 deletion(-)

diff --git a/mm/hugetlb.c b/mm/hugetlb.c
index 26ab9dfc7d63..3158a55ce567 100644
--- a/mm/hugetlb.c
+++ b/mm/hugetlb.c
@@ -3247,9 +3247,12 @@ struct folio *alloc_hugetlb_folio(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);
 			hugetlb_cgroup_uncharge_folio_rsvd(hstate_index(h),
 					pages_per_huge_page(h), folio);
+			spin_unlock_irq(&hugetlb_lock);
+		}
 	}
 
 	if (!memcg_charge_ret)
-- 
2.44.0