From patchwork Wed Jul 18 22:58:44 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Omar Sandoval X-Patchwork-Id: 10533407 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 D4D5C6020A for ; Wed, 18 Jul 2018 22:59:21 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C7369298B0 for ; Wed, 18 Jul 2018 22:59:21 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id BB898298BD; Wed, 18 Jul 2018 22:59:21 +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=ham 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 3BCF5298B0 for ; Wed, 18 Jul 2018 22:59:21 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730369AbeGRXjZ (ORCPT ); Wed, 18 Jul 2018 19:39:25 -0400 Received: from mail-pl0-f65.google.com ([209.85.160.65]:37548 "EHLO mail-pl0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1730329AbeGRXjY (ORCPT ); Wed, 18 Jul 2018 19:39:24 -0400 Received: by mail-pl0-f65.google.com with SMTP id 31-v6so2694140plc.4 for ; Wed, 18 Jul 2018 15:59:18 -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=jejP2yrNUB7zHbhkc1Ji+iKVjXdsuDSSW0aNb0+t3w4=; b=f+s9HaIKDBRWut27nGIZf0trUyVObUF0NZNm3n9F/WbYwoe9Qa/97x88Xsv1K+Q8sx 7Hegh0w9kCaz+qvzuPGZels/4S2fKNl2dwvrogcKLID8QS2OM2fzSYoayafhKxG6SLv3 oWdKJRoirkfDo6lSJsIXe12CwquoFRky13TDCcdRGgHIMkRR08w3oYO6SbI3lzmCr5iR u7pHMQCQmfto7ITsVtklBOYeGnVjtJkim4SBvvX2OSWQGg+5veAZhUBYupbzlnWoUfV4 PX9WB9HihSR3pnbKl5PYj3f4al+o8fqEvLBw9qC+IygUkJkVSmHyJbcntLuuLh4aZQOV ox/A== 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=jejP2yrNUB7zHbhkc1Ji+iKVjXdsuDSSW0aNb0+t3w4=; b=bTPRKieLgpNYBgbeGdzlDJf8agRTKSkLEv2wAzPrjsEgflvjKt+4RZ6wIUt3KAYI2T YaV7a0DyM48ZwzP/jFOMXzkL5LARJX5xH3bU43c7YfMsoEtC+x3oQkl3+PgdrMsYYfLe +RGaVZ4lPZe23sCen9SsAd/DXHE4+0dHuN9kk7GAPYi3oWny6mSOKn5PwxCmQ2t7YQI9 K525Xq/QYxDnZCvOLPtsTo+rxxJ5kgVYfxGE7e9tFm8dn6eidRY9edEq547UjKxUFkyK 06wZ5Pd6qhHn9TDlwIBFCy2+9fBnJZ5sJlT9HcyExe/qip0ILl5FH5ASDJJPef3aSJ0Q mUQA== X-Gm-Message-State: AOUpUlHBr8aNdVKPWhXavyBgzulc8K9wY1QpIGFV77CrQnujuAJ+HrdH SbrXdAAjhs471chlOy2dMdOz3g== X-Google-Smtp-Source: AAOMgpdXPuDFIZOHhzyEcxMEilCk1HaJHcsSMImSWszc9RqS26Q2wZj15mKiQxXDJXxBNfTbfAATVg== X-Received: by 2002:a17:902:9681:: with SMTP id n1-v6mr7907532plp.244.1531954757740; Wed, 18 Jul 2018 15:59:17 -0700 (PDT) Received: from vader.hsd1.wa.comcast.net ([2601:602:8800:a9a9:e6a7:a0ff:fe0b:c9a8]) by smtp.gmail.com with ESMTPSA id s16-v6sm6377946pfm.114.2018.07.18.15.59.16 (version=TLS1_2 cipher=ECDHE-RSA-AES128-GCM-SHA256 bits=128/128); Wed, 18 Jul 2018 15:59:17 -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 v3 4/8] proc/kcore: fix memory hotplug vs multiple opens race Date: Wed, 18 Jul 2018 15:58:44 -0700 Message-Id: <6106c509998779730c12400c1b996425df7d7089.1531953780.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 ae43a97d511d..95aa988c5b5d 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 (xchg(&kcore_need_update, 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 (!xchg(&kcore_need_update, 0)) + goto out; + + ret = kcore_ram_list(&list); + if (ret) { + /* Couldn't get the RAM list, try again next time. */ + WRITE_ONCE(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 */ /*****************************************************************************/ /*