From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-8.2 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, URIBL_BLOCKED,USER_AGENT_SANE_1 autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 0B6B3CA9EA0 for ; Sat, 26 Oct 2019 02:03:57 +0000 (UTC) Received: from kanga.kvack.org (kanga.kvack.org [205.233.56.17]) by mail.kernel.org (Postfix) with ESMTP id CAF7221D7F for ; Sat, 26 Oct 2019 02:03:56 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org CAF7221D7F Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=huawei.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=owner-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix) id 670DC6B0006; Fri, 25 Oct 2019 22:03:56 -0400 (EDT) Received: by kanga.kvack.org (Postfix, from userid 40) id 6213E6B0008; Fri, 25 Oct 2019 22:03:56 -0400 (EDT) X-Delivered-To: int-list-linux-mm@kvack.org Received: by kanga.kvack.org (Postfix, from userid 63042) id 535EC6B000A; Fri, 25 Oct 2019 22:03:56 -0400 (EDT) X-Delivered-To: linux-mm@kvack.org Received: from forelay.hostedemail.com (smtprelay0079.hostedemail.com [216.40.44.79]) by kanga.kvack.org (Postfix) with ESMTP id 2D07B6B0006 for ; Fri, 25 Oct 2019 22:03:56 -0400 (EDT) Received: from smtpin16.hostedemail.com (10.5.19.251.rfc1918.com [10.5.19.251]) by forelay02.hostedemail.com (Postfix) with SMTP id B72501EF0 for ; Sat, 26 Oct 2019 02:03:55 +0000 (UTC) X-FDA: 76084290030.16.shock06_3f37d6818c322 X-HE-Tag: shock06_3f37d6818c322 X-Filterd-Recvd-Size: 5117 Received: from huawei.com (szxga05-in.huawei.com [45.249.212.191]) by imf47.hostedemail.com (Postfix) with ESMTP for ; Sat, 26 Oct 2019 02:03:54 +0000 (UTC) Received: from DGGEMS401-HUB.china.huawei.com (unknown [172.30.72.58]) by Forcepoint Email with ESMTP id BAD7660D273AAC2C1959; Sat, 26 Oct 2019 10:03:50 +0800 (CST) Received: from [127.0.0.1] (10.133.219.218) by DGGEMS401-HUB.china.huawei.com (10.3.19.201) with Microsoft SMTP Server id 14.3.439.0; Sat, 26 Oct 2019 10:03:49 +0800 Message-ID: <5DB3A985.4000903@huawei.com> Date: Sat, 26 Oct 2019 10:03:49 +0800 From: zhong jiang User-Agent: Mozilla/5.0 (Windows NT 6.1; WOW64; rv:12.0) Gecko/20120428 Thunderbird/12.0.1 MIME-Version: 1.0 To: Matthew Wilcox , CC: , , , Subject: Re: [PATCH 4.19] memfd: Fix locking when tagging pins References: <20191025165837.22979-1-willy@infradead.org> In-Reply-To: <20191025165837.22979-1-willy@infradead.org> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 7bit X-Originating-IP: [10.133.219.218] X-CFilter-Loop: Reflected 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 2019/10/26 0:58, Matthew Wilcox wrote: > From: "Matthew Wilcox (Oracle)" > > The RCU lock is insufficient to protect the radix tree iteration as > a deletion from the tree can occur before we take the spinlock to > tag the entry. In 4.19, this has manifested as a bug with the following > trace: > > kernel BUG at lib/radix-tree.c:1429! > invalid opcode: 0000 [#1] SMP KASAN PTI > CPU: 7 PID: 6935 Comm: syz-executor.2 Not tainted 4.19.36 #25 > Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS 1.10.2-1ubuntu1 04/01/2014 > RIP: 0010:radix_tree_tag_set+0x200/0x2f0 lib/radix-tree.c:1429 > Code: 00 00 5b 5d 41 5c 41 5d 41 5e 41 5f c3 48 89 44 24 10 e8 a3 29 7e fe 48 8b 44 24 10 48 0f ab 03 e9 d2 fe ff ff e8 90 29 7e fe <0f> 0b 48 c7 c7 e0 5a 87 84 e8 f0 e7 08 ff 4c 89 ef e8 4a ff ac fe > RSP: 0018:ffff88837b13fb60 EFLAGS: 00010016 > RAX: 0000000000040000 RBX: ffff8883c5515d58 RCX: ffffffff82cb2ef0 > RDX: 0000000000000b72 RSI: ffffc90004cf2000 RDI: ffff8883c5515d98 > RBP: ffff88837b13fb98 R08: ffffed106f627f7e R09: ffffed106f627f7e > R10: 0000000000000001 R11: ffffed106f627f7d R12: 0000000000000004 > R13: ffffea000d7fea80 R14: 1ffff1106f627f6f R15: 0000000000000002 > FS: 00007fa1b8df2700(0000) GS:ffff8883e2fc0000(0000) knlGS:0000000000000000 > CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > CR2: 00007fa1b8df1db8 CR3: 000000037d4d2001 CR4: 0000000000160ee0 > Call Trace: > memfd_tag_pins mm/memfd.c:51 [inline] > memfd_wait_for_pins+0x2c5/0x12d0 mm/memfd.c:81 > memfd_add_seals mm/memfd.c:215 [inline] > memfd_fcntl+0x33d/0x4a0 mm/memfd.c:247 > do_fcntl+0x589/0xeb0 fs/fcntl.c:421 > __do_sys_fcntl fs/fcntl.c:463 [inline] > __se_sys_fcntl fs/fcntl.c:448 [inline] > __x64_sys_fcntl+0x12d/0x180 fs/fcntl.c:448 > do_syscall_64+0xc8/0x580 arch/x86/entry/common.c:293 > > The problem does not occur in mainline due to the XArray rewrite which > changed the locking to exclude modification of the tree during iteration. > At the time, nobody realised this was a bugfix. Backport the locking > changes to stable. > > Cc: stable@vger.kernel.org > Reported-by: zhong jiang > Signed-off-by: Matthew Wilcox (Oracle) > --- > mm/memfd.c | 18 ++++++++++-------- > 1 file changed, 10 insertions(+), 8 deletions(-) > > diff --git a/mm/memfd.c b/mm/memfd.c > index 2bb5e257080e..5859705dafe1 100644 > --- a/mm/memfd.c > +++ b/mm/memfd.c > @@ -34,11 +34,12 @@ static void memfd_tag_pins(struct address_space *mapping) > void __rcu **slot; > pgoff_t start; > struct page *page; > + unsigned int tagged = 0; > > lru_add_drain(); > start = 0; > - rcu_read_lock(); > > + xa_lock_irq(&mapping->i_pages); > radix_tree_for_each_slot(slot, &mapping->i_pages, &iter, start) { > page = radix_tree_deref_slot(slot); > if (!page || radix_tree_exception(page)) { > @@ -47,18 +48,19 @@ static void memfd_tag_pins(struct address_space *mapping) > continue; > } > } else if (page_count(page) - page_mapcount(page) > 1) { > - xa_lock_irq(&mapping->i_pages); > radix_tree_tag_set(&mapping->i_pages, iter.index, > MEMFD_TAG_PINNED); > - xa_unlock_irq(&mapping->i_pages); > } > > - if (need_resched()) { > - slot = radix_tree_iter_resume(slot, &iter); > - cond_resched_rcu(); > - } > + if (++tagged % 1024) > + continue; > + > + slot = radix_tree_iter_resume(slot, &iter); > + xa_unlock_irq(&mapping->i_pages); > + cond_resched(); > + xa_lock_irq(&mapping->i_pages); > } > - rcu_read_unlock(); > + xa_unlock_irq(&mapping->i_pages); > } > > /* The patch looks good to me. thanks for your review and efforts. Sasha, The patch was correct, It should go into stable instead of my patch. Sincerely, zhong jiang