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[175.177.40.153]) by smtp.gmail.com with ESMTPSA id q8sm4201339pfk.137.2021.04.28.00.46.56 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 28 Apr 2021 00:46:58 -0700 (PDT) Date: Wed, 28 Apr 2021 16:46:54 +0900 From: Naoya Horiguchi To: Mike Kravetz , Michal Hocko , Muchun Song , "akpm@linux-foundation.org" , "osalvador@suse.de" , "linux-mm@kvack.org" Cc: "linux-kernel@vger.kernel.org" , Naoya Horiguchi Subject: [PATCH] mm,hwpoison: fix race with compound page allocation Message-ID: <20210428074654.GA2093897@u2004> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210423080153.GA78658@hori.linux.bs1.fc.nec.co.jp> X-Rspamd-Server: rspam03 X-Rspamd-Queue-Id: 0AE0512E X-Stat-Signature: 7jgmwitc4qmwh4toddc78rs13toujdt5 Received-SPF: none (gmail.com>: No applicable sender policy available) receiver=imf12; identity=mailfrom; envelope-from=""; helo=mail-pg1-f172.google.com; client-ip=209.85.215.172 X-HE-DKIM-Result: pass/pass X-HE-Tag: 1619596008-299112 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 Fri, Apr 23, 2021 at 08:01:54AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote: > On Thu, Apr 22, 2021 at 08:27:46AM +0000, HORIGUCHI NAOYA(堀口 直也) wrote: > > On Wed, Apr 21, 2021 at 11:03:24AM -0700, Mike Kravetz wrote: > > > On 4/21/21 1:33 AM, HORIGUCHI NAOYA(堀口 直也) wrote: > > > > On Wed, Apr 21, 2021 at 10:03:34AM +0200, Michal Hocko wrote: > > > >> [Cc Naoya] > > > >> > > > >> On Wed 21-04-21 14:02:59, Muchun Song wrote: > > > >>> The possible bad scenario: > > > >>> > > > >>> CPU0: CPU1: > > > >>> > > > >>> gather_surplus_pages() > > > >>> page = alloc_surplus_huge_page() > > > >>> memory_failure_hugetlb() > > > >>> get_hwpoison_page(page) > > > >>> __get_hwpoison_page(page) > > > >>> get_page_unless_zero(page) > > > >>> zero = put_page_testzero(page) > > > >>> VM_BUG_ON_PAGE(!zero, page) > > > >>> enqueue_huge_page(h, page) > > > >>> put_page(page) > > > >>> > > > >>> The refcount can possibly be increased by memory-failure or soft_offline > > > >>> handlers, we can trigger VM_BUG_ON_PAGE and wrongly add the page to the > > > >>> hugetlb pool list. > > > >> > > > >> The hwpoison side of this looks really suspicious to me. It shouldn't > > > >> really touch the reference count of hugetlb pages without being very > > > >> careful (and having hugetlb_lock held). > > > > > > > > I have the same feeling, there is a window where a hugepage is refcounted > > > > during converting from buddy free pages into free hugepage, so refcount > > > > alone is not enough to prevent the race. hugetlb_lock is retaken after > > > > alloc_surplus_huge_page returns, so simply holding hugetlb_lock in > > > > get_hwpoison_page() seems not work. Is there any status bit to show that a > > > > hugepage is just being initialized (not in free hugepage pool or in use)? > > > > > > > > > > It seems we can also race with the code that makes a compound page a > > > hugetlb page. The memory failure code could be called after allocating > > > pages from buddy and before setting compound page DTOR. So, the memory > > > handling code will process it as a compound page. > > > > Yes, so get_hwpoison_page() has to call get_page_unless_zero() > > only when memory_failure() can surely handle the error. > > > > > > > > Just thinking that this may not be limited to the hugetlb specific memory > > > failure handling? > > > > Currently hugetlb page is the only type of compound page supported by memory > > failure. But I agree with you that other types of compound pages have the > > same race window, and judging only with get_page_unless_zero() is dangerous. > > So I think that __get_hwpoison_page() should have the following structure: > > > > if (PageCompound) { > > if (PageHuge) { > > if (PageHugeFreed || PageHugeActive) { > > if (get_page_unless_zero) > > return 0; // path for in-use hugetlb page > > else > > return 1; // path for free hugetlb page > > } else { > > return -EBUSY; // any transient hugetlb page > > } > > } else { > > ... // any other compound page (like thp, slab, ...) > > } > > } else { > > ... // any non-compound page > > } > > The above pseudo code was wrong, so let me update my thought. > I'm now trying to solve the reported issue by changing __get_hwpoison_page() > like below: > > static int __get_hwpoison_page(struct page *page) > { > struct page *head = compound_head(page); > > if (PageCompound(page)) { > if (PageSlab(page)) { > return get_page_unless_zero(page); > } else if (PageHuge(head)) { > if (HPageFreed(head) || HPageMigratable(head)) > return get_page_unless_zero(head); > } else if (PageTransHuge(head)) { > /* > * Non anonymous thp exists only in allocation/free time. We > * can't handle such a case correctly, so let's give it up. > * This should be better than triggering BUG_ON when kernel > * tries to touch the "partially handled" page. > */ > if (!PageAnon(head)) { > pr_err("Memory failure: %#lx: non anonymous thp\n", > page_to_pfn(page)); > return 0; > } > if (get_page_unless_zero(head)) { > if (head == compound_head(page)) > return 1; > pr_info("Memory failure: %#lx cannot catch tail\n", > page_to_pfn(page)); > put_page(head); > } > } > return 0; > } > > return get_page_unless_zero(page); > } > > Some notes: > > - in hugetlb path, new HPage* checks should avoid the reported race, > but I still need more testing to confirm it, > - PageSlab check is added because otherwise I found that "non anonymous thp" > path is chosen, that's obviously wrong, > - thp's branch has a known issue unrelated to the current issue, which > will/should be improved later. > > I'll send a patch next week. I confirmed that the patch fixes the reported problem (in the testcase triggering VM_BUG_ON_PAGE() without this patch). So let me suggest this as a fix on hwpoison side. Thanks, Naoya Horiguchi --- From: Naoya Horiguchi Date: Wed, 28 Apr 2021 15:55:47 +0900 Subject: [PATCH] mm,hwpoison: fix race with compound page allocation When hugetlb page fault (under overcommiting situation) and memory_failure() race, VM_BUG_ON_PAGE() is triggered by the following race: CPU0: CPU1: gather_surplus_pages() page = alloc_surplus_huge_page() memory_failure_hugetlb() get_hwpoison_page(page) __get_hwpoison_page(page) get_page_unless_zero(page) zero = put_page_testzero(page) VM_BUG_ON_PAGE(!zero, page) enqueue_huge_page(h, page) put_page(page) __get_hwpoison_page() only checks page refcount before taking additional one for memory error handling, which is wrong because there's time windows where compound pages have non-zero refcount during initialization. So makes __get_hwpoison_page() check more page status for a few types of compound pages. PageSlab() check is added because otherwise "non anonymous thp" path is wrongly chosen for slab pages. Signed-off-by: Naoya Horiguchi Reported-by: Muchun Song --- mm/memory-failure.c | 48 +++++++++++++++++++++++++-------------------- 1 file changed, 27 insertions(+), 21 deletions(-) diff --git a/mm/memory-failure.c b/mm/memory-failure.c index a3659619d293..61988e332712 100644 --- a/mm/memory-failure.c +++ b/mm/memory-failure.c @@ -1095,30 +1095,36 @@ static int __get_hwpoison_page(struct page *page) { struct page *head = compound_head(page); - if (!PageHuge(head) && PageTransHuge(head)) { - /* - * Non anonymous thp exists only in allocation/free time. We - * can't handle such a case correctly, so let's give it up. - * This should be better than triggering BUG_ON when kernel - * tries to touch the "partially handled" page. - */ - if (!PageAnon(head)) { - pr_err("Memory failure: %#lx: non anonymous thp\n", - page_to_pfn(page)); - return 0; + if (PageCompound(page)) { + if (PageSlab(page)) { + return get_page_unless_zero(page); + } else if (PageHuge(head)) { + if (HPageFreed(head) || HPageMigratable(head)) + return get_page_unless_zero(head); + } else if (PageTransHuge(head)) { + /* + * Non anonymous thp exists only in allocation/free time. We + * can't handle such a case correctly, so let's give it up. + * This should be better than triggering BUG_ON when kernel + * tries to touch the "partially handled" page. + */ + if (!PageAnon(head)) { + pr_err("Memory failure: %#lx: non anonymous thp\n", + page_to_pfn(page)); + return 0; + } + if (get_page_unless_zero(head)) { + if (head == compound_head(page)) + return 1; + pr_info("Memory failure: %#lx cannot catch tail\n", + page_to_pfn(page)); + put_page(head); + } } + return 0; } - if (get_page_unless_zero(head)) { - if (head == compound_head(page)) - return 1; - - pr_info("Memory failure: %#lx cannot catch tail\n", - page_to_pfn(page)); - put_page(head); - } - - return 0; + return get_page_unless_zero(page); } /*