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dkim=pass header.d=google.com header.s=20210112 header.b=JTa7n5j0; spf=pass (imf07.hostedemail.com: domain of jthoughton@google.com designates 209.85.208.178 as permitted sender) smtp.mailfrom=jthoughton@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam01 X-HE-Tag: 1667412255-117157 X-Bogosity: Ham, tests=bogofilter, spamicity=0.000000, version=1.2.4 Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: On Sun, Oct 30, 2022 at 2:30 PM Peter Xu wrote: > > RCU makes sure the pte_t* won't go away from under us. Please refer to the > comment above huge_pte_offset() for more information. Thanks for this series, Peter! :) > > Signed-off-by: Peter Xu > --- > mm/hugetlb.c | 6 +++++- > 1 file changed, 5 insertions(+), 1 deletion(-) > > diff --git a/mm/hugetlb.c b/mm/hugetlb.c > index 5dc87e4e6780..6d336d286394 100644 > --- a/mm/hugetlb.c > +++ b/mm/hugetlb.c > @@ -5822,6 +5822,8 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > int need_wait_lock = 0; > unsigned long haddr = address & huge_page_mask(h); > > + /* For huge_pte_offset() */ > + rcu_read_lock(); > ptep = huge_pte_offset(mm, haddr, huge_page_size(h)); > if (ptep) { > /* > @@ -5830,13 +5832,15 @@ vm_fault_t hugetlb_fault(struct mm_struct *mm, struct vm_area_struct *vma, > * not actually modifying content here. > */ > entry = huge_ptep_get(ptep); > + rcu_read_unlock(); > if (unlikely(is_hugetlb_entry_migration(entry))) { > migration_entry_wait_huge(vma, ptep); ptep is used here (and we dereference it in `__migration_entry_wait_huge`), so this looks unsafe to me. A simple way to fix this would be to move the migration entry check after the huge_pte_alloc call. - James > return 0; > } else if (unlikely(is_hugetlb_entry_hwpoisoned(entry))) > return VM_FAULT_HWPOISON_LARGE | > VM_FAULT_SET_HINDEX(hstate_index(h)); > - } > + } else > + rcu_read_unlock(); > > /* > * Serialize hugepage allocation and instantiation, so that we don't > -- > 2.37.3 >