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dkim=pass header.d=google.com header.s=20210112 header.b=jd3KIXC0; spf=pass (imf29.hostedemail.com: domain of jthoughton@google.com designates 209.85.128.169 as permitted sender) smtp.mailfrom=jthoughton@google.com; dmarc=pass (policy=reject) header.from=google.com X-Rspamd-Server: rspam01 X-HE-Tag: 1667412389-983770 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 2:29 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. > > Signed-off-by: Peter Xu > --- > fs/userfaultfd.c | 4 ++++ > 1 file changed, 4 insertions(+) > > diff --git a/fs/userfaultfd.c b/fs/userfaultfd.c > index 07c81ab3fd4d..4e813e68e4f8 100644 > --- a/fs/userfaultfd.c > +++ b/fs/userfaultfd.c > @@ -243,6 +243,9 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, > > mmap_assert_locked(mm); > > + /* For huge_pte_offset() */ > + rcu_read_lock(); userfaultfd_huge_must_wait is called after we set the task's state to blocking. Is it always safe to call rcu_read_lock (and rcu_read_unlock) in this case? (With my basic understanding of RCU, this seems like it should be safe, but I'm not sure.) - James > + > ptep = huge_pte_offset(mm, address, vma_mmu_pagesize(vma)); > > if (!ptep) > @@ -261,6 +264,7 @@ static inline bool userfaultfd_huge_must_wait(struct userfaultfd_ctx *ctx, > if (!huge_pte_write(pte) && (reason & VM_UFFD_WP)) > ret = true; > out: > + rcu_read_unlock(); > return ret; > } > #else > -- > 2.37.3 >