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Sun, 19 Jun 2022 23:42:06 -0700 (PDT) X-Google-Smtp-Source: AGRyM1vayy0dcfFwO7ndztwu/0c7V86tRzzO8t/BWwPdFrAopmGRmWzudi9T0GZvGPOV8ZY7FB73/A== X-Received: by 2002:a63:3608:0:b0:40c:a38e:2a3b with SMTP id d8-20020a633608000000b0040ca38e2a3bmr5229633pga.31.1655707325972; Sun, 19 Jun 2022 23:42:05 -0700 (PDT) Received: from [10.72.12.43] ([209.132.188.80]) by smtp.gmail.com with ESMTPSA id b9-20020a17090aa58900b001e2f6c7b6f6sm7379811pjq.10.2022.06.19.23.42.02 (version=TLS1_3 cipher=TLS_AES_128_GCM_SHA256 bits=128/128); Sun, 19 Jun 2022 23:42:05 -0700 (PDT) Subject: Re: [PATCH 3/3] mm: Clear page->private when splitting or migrating a page To: "Matthew Wilcox (Oracle)" Cc: linux-kernel@vger.kernel.org, linux-mm@kvack.org, linux-fsdevel@vger.kernel.org References: <20220619151143.1054746-1-willy@infradead.org> <20220619151143.1054746-4-willy@infradead.org> From: Xiubo Li Message-ID: <2031fee3-e09a-5cea-be26-71360893d161@redhat.com> Date: Mon, 20 Jun 2022 14:41:58 +0800 User-Agent: Mozilla/5.0 (X11; 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imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=CIpzXEEd; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf17.hostedemail.com: domain of xiubli@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=xiubli@redhat.com Authentication-Results: imf17.hostedemail.com; dkim=pass header.d=redhat.com header.s=mimecast20190719 header.b=CIpzXEEd; dmarc=pass (policy=none) header.from=redhat.com; spf=none (imf17.hostedemail.com: domain of xiubli@redhat.com has no SPF policy when checking 170.10.133.124) smtp.mailfrom=xiubli@redhat.com X-Rspamd-Server: rspam12 X-Rspam-User: X-Stat-Signature: 8yx8te4cs5j5ut7anwjpn1r41ck6z1a1 X-Rspamd-Queue-Id: 1D3704000C X-HE-Tag: 1655707331-689039 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 6/19/22 11:11 PM, Matthew Wilcox (Oracle) wrote: > In our efforts to remove uses of PG_private, we have found folios with > the private flag clear and folio->private not-NULL. That is the root > cause behind 642d51fb0775 ("ceph: check folio PG_private bit instead > of folio->private"). It can also affect a few other filesystems that > haven't yet reported a problem. > > compaction_alloc() can return a page with uninitialised page->private, > and rather than checking all the callers of migrate_pages(), just zero > page->private after calling get_new_page(). Similarly, the tail pages > from split_huge_page() may also have an uninitialised page->private. > > Reported-by: Xiubo Li > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/huge_memory.c | 1 + > mm/migrate.c | 1 + > 2 files changed, 2 insertions(+) > > diff --git a/mm/huge_memory.c b/mm/huge_memory.c > index f7248002dad9..9b31a50217b5 100644 > --- a/mm/huge_memory.c > +++ b/mm/huge_memory.c > @@ -2377,6 +2377,7 @@ static void __split_huge_page_tail(struct page *head, int tail, > page_tail); > page_tail->mapping = head->mapping; > page_tail->index = head->index + tail; > + page_tail->private = NULL; There has a warning when compiling it: mm/huge_memory.c: In function ‘__split_huge_page_tail’: mm/huge_memory.c:2380:21: warning: assignment to ‘long unsigned int’ from ‘void *’ makes integer from pointer without a cast [-Wint-conversion]   page_tail->private = NULL;                      ^   AR      mm/built-in.a > > /* Page flags must be visible before we make the page non-compound. */ > smp_wmb(); > diff --git a/mm/migrate.c b/mm/migrate.c > index e51588e95f57..6c1ea61f39d8 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -1106,6 +1106,7 @@ static int unmap_and_move(new_page_t get_new_page, > if (!newpage) > return -ENOMEM; > > + newpage->private = 0; > rc = __unmap_and_move(page, newpage, force, mode); > if (rc == MIGRATEPAGE_SUCCESS) > set_page_owner_migrate_reason(newpage, reason);