From patchwork Fri Jul 13 00:09:35 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Omar Sandoval X-Patchwork-Id: 10522457 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id 7E2A5602A0 for ; Fri, 13 Jul 2018 00:10:23 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6EDB42965D for ; Fri, 13 Jul 2018 00:10:23 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 6393A296CA; Fri, 13 Jul 2018 00:10:23 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID, MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=unavailable version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id E4BA62965D for ; Fri, 13 Jul 2018 00:10:22 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2387886AbeGMAWS (ORCPT ); Thu, 12 Jul 2018 20:22:18 -0400 Received: from mail-pf0-f194.google.com ([209.85.192.194]:36923 "EHLO mail-pf0-f194.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387767AbeGMAVq (ORCPT ); Thu, 12 Jul 2018 20:21:46 -0400 Received: by mail-pf0-f194.google.com with SMTP id x10-v6so11662314pfm.4 for ; Thu, 12 Jul 2018 17:09:49 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=osandov-com.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:in-reply-to:references; bh=3CKNrbqL5MSp604wgy3UdOg6ForL/ongmOzBrmUluMQ=; b=KyJTdKSPYy6UeZ5TZ+Zk0cFo8XfOmCc8HkTP21MumlzE9DbGiA8PjdE+gEUX16Ruz6 1HvWeKT42njZW2vfD0mAmM79OFgTq6TYO9klFlMw+skXDxCP4TB+lGNPPkDLpB6vYZLV n/tk7dBeHM/umrJJmDjZ2nPKZ3vJx8AvV6nrPis5bGYY489ohgBgeRORU2wLg3B1Bfcx WYTBHFS7TytyIBr0Mhwy8MLJbbFrFBnVeT0Ph2Bg8QVHYqGuJk0J3yBBFKfE7gRrRb7M NLVhZYSrLGrOLDJPAhJiDczXpRy0ef7vy3Fp7yPdI/qI+QUx0/rA2+GAAXOLGemT9uW9 Wgqw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:in-reply-to :references; bh=3CKNrbqL5MSp604wgy3UdOg6ForL/ongmOzBrmUluMQ=; b=gcPJB2XUWjQdttMaK2N7vAbWiTdrlh9p7/BbZyvI7sqVFqn4LD+3A6u3sRRJ2ryyDT iSp8l2d7bhBYDbb++B9Qyz+XZq+42CFWOLlmOEEZgAtejVdM46B2Hf7A0zM2TGKwMYaJ jNzciSYTpidYAfRN52d98BXFLLW4SAcQkeoy2wpXI4uhHbFiW9hbk+XTV3JBdfHccNTP 4BSqYlmuRgu0U/lXAKhiAUrJKKQdInKHJ+bPimui32G8qnNn4G+TYf26pVHCwRBSbkFb v+orCovCDKuWGIMhGi88YXEf5pxpiJ6pLYIORzXcg/yzpGKle0JpGjsa0dGzrMcKgOfV /RVg== X-Gm-Message-State: AOUpUlEYJf8Bj7PJSKfMW8wuQiVFYR+a616/SDRXx/wy4pTxYHV3jE4I RrZn+oeWXY9rOCKu6LsVKik9WWtyT8M= X-Google-Smtp-Source: AAOMgpcaAutMMWZNjqQoLffBS3XTFNjFVCEOIfy10jurBnZjq4/0Isdm6FtBtc16utOMB3KdEXgVhw== X-Received: by 2002:a62:642:: with SMTP id 63-v6mr4603759pfg.222.1531440588940; Thu, 12 Jul 2018 17:09:48 -0700 (PDT) Received: from vader.thefacebook.com ([2620:10d:c090:200::5:74a0]) by smtp.gmail.com with ESMTPSA id b86-v6sm4452067pfj.35.2018.07.12.17.09.48 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Thu, 12 Jul 2018 17:09:48 -0700 (PDT) From: Omar Sandoval To: linux-kernel@vger.kernel.org, linux-fsdevel@vger.kernel.org, Andrew Morton Cc: Alexey Dobriyan , Eric Biederman , James Morse , Bhupesh Sharma , kernel-team@fb.com Subject: [PATCH v2 3/7] proc/kcore: fix memory hotplug vs multiple opens race Date: Thu, 12 Jul 2018 17:09:35 -0700 Message-Id: <87df7359270e708d2e599ca0c9011c9347522c50.1531440458.git.osandov@fb.com> X-Mailer: git-send-email 2.18.0 In-Reply-To: References: Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP From: Omar Sandoval There's a theoretical race condition that will cause /proc/kcore to miss a memory hotplug event: CPU0 CPU1 // hotplug event 1 kcore_need_update = 1 open_kcore() open_kcore() kcore_update_ram() kcore_update_ram() // Walk RAM // Walk RAM __kcore_update_ram() __kcore_update_ram() kcore_need_update = 0 // hotplug event 2 kcore_need_update = 1 kcore_need_update = 0 Note that CPU1 set up the RAM kcore entries with the state after hotplug event 1 but cleared the flag for hotplug event 2. The RAM entries will therefore be stale until there is another hotplug event. This is an extremely unlikely sequence of events, but the fix makes the synchronization saner, anyways: we serialize the entire update sequence, which means that whoever clears the flag will always succeed in replacing the kcore list. Signed-off-by: Omar Sandoval --- fs/proc/kcore.c | 93 +++++++++++++++++++++++-------------------------- 1 file changed, 44 insertions(+), 49 deletions(-) diff --git a/fs/proc/kcore.c b/fs/proc/kcore.c index def92fccb167..33667db6e370 100644 --- a/fs/proc/kcore.c +++ b/fs/proc/kcore.c @@ -98,53 +98,15 @@ static size_t get_kcore_size(int *nphdr, size_t *elf_buflen) return size + *elf_buflen; } -static void free_kclist_ents(struct list_head *head) -{ - struct kcore_list *tmp, *pos; - - list_for_each_entry_safe(pos, tmp, head, list) { - list_del(&pos->list); - kfree(pos); - } -} -/* - * Replace all KCORE_RAM/KCORE_VMEMMAP information with passed list. - */ -static void __kcore_update_ram(struct list_head *list) -{ - int nphdr; - size_t size; - struct kcore_list *tmp, *pos; - LIST_HEAD(garbage); - - down_write(&kclist_lock); - if (atomic_cmpxchg(&kcore_need_update, 1, 0)) { - list_for_each_entry_safe(pos, tmp, &kclist_head, list) { - if (pos->type == KCORE_RAM - || pos->type == KCORE_VMEMMAP) - list_move(&pos->list, &garbage); - } - list_splice_tail(list, &kclist_head); - } else - list_splice(list, &garbage); - proc_root_kcore->size = get_kcore_size(&nphdr, &size); - up_write(&kclist_lock); - - free_kclist_ents(&garbage); -} - - #ifdef CONFIG_HIGHMEM /* * If no highmem, we can assume [0...max_low_pfn) continuous range of memory * because memory hole is not as big as !HIGHMEM case. * (HIGHMEM is special because part of memory is _invisible_ from the kernel.) */ -static int kcore_update_ram(void) +static int kcore_ram_list(struct list_head *head) { - LIST_HEAD(head); struct kcore_list *ent; - int ret = 0; ent = kmalloc(sizeof(*ent), GFP_KERNEL); if (!ent) @@ -152,9 +114,8 @@ static int kcore_update_ram(void) ent->addr = (unsigned long)__va(0); ent->size = max_low_pfn << PAGE_SHIFT; ent->type = KCORE_RAM; - list_add(&ent->list, &head); - __kcore_update_ram(&head); - return ret; + list_add(&ent->list, head); + return 0; } #else /* !CONFIG_HIGHMEM */ @@ -253,11 +214,10 @@ kclist_add_private(unsigned long pfn, unsigned long nr_pages, void *arg) return 1; } -static int kcore_update_ram(void) +static int kcore_ram_list(struct list_head *list) { int nid, ret; unsigned long end_pfn; - LIST_HEAD(head); /* Not inialized....update now */ /* find out "max pfn" */ @@ -269,15 +229,50 @@ static int kcore_update_ram(void) end_pfn = node_end; } /* scan 0 to max_pfn */ - ret = walk_system_ram_range(0, end_pfn, &head, kclist_add_private); - if (ret) { - free_kclist_ents(&head); + ret = walk_system_ram_range(0, end_pfn, list, kclist_add_private); + if (ret) return -ENOMEM; + return 0; +} +#endif /* CONFIG_HIGHMEM */ + +static int kcore_update_ram(void) +{ + LIST_HEAD(list); + LIST_HEAD(garbage); + int nphdr; + size_t size; + struct kcore_list *tmp, *pos; + int ret = 0; + + down_write(&kclist_lock); + if (!atomic_cmpxchg(&kcore_need_update, 1, 0)) + goto out; + + ret = kcore_ram_list(&list); + if (ret) { + /* Couldn't get the RAM list, try again next time. */ + atomic_set(&kcore_need_update, 1); + list_splice_tail(&list, &garbage); + goto out; + } + + list_for_each_entry_safe(pos, tmp, &kclist_head, list) { + if (pos->type == KCORE_RAM || pos->type == KCORE_VMEMMAP) + list_move(&pos->list, &garbage); + } + list_splice_tail(&list, &kclist_head); + + proc_root_kcore->size = get_kcore_size(&nphdr, &size); + +out: + up_write(&kclist_lock); + list_for_each_entry_safe(pos, tmp, &garbage, list) { + list_del(&pos->list); + kfree(pos); } - __kcore_update_ram(&head); return ret; } -#endif /* CONFIG_HIGHMEM */ /*****************************************************************************/ /*