From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752828AbbCOQOu (ORCPT ); Sun, 15 Mar 2015 12:14:50 -0400 Received: from mout.gmx.net ([212.227.17.20]:59417 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752670AbbCOQOr (ORCPT ); Sun, 15 Mar 2015 12:14:47 -0400 From: Heinrich Schuchardt To: Andrew Morton Cc: Aaron Tomlin , Andy Lutomirski , Davidlohr Bueso , David Rientjes , "David S. Miller" , Fabian Frederick , Guenter Roeck , "H. Peter Anvin" , Ingo Molnar , Jens Axboe , Joe Perches , Johannes Weiner , Jonathan Corbet , Kees Cook , Michael Marineau , Oleg Nesterov , "Paul E. McKenney" , Peter Zijlstra , Prarit Bhargava , Rik van Riel , Rusty Russell , Steven Rostedt , Thomas Gleixner , Vladimir Davydov , linux-kernel@vger.kernel.org, linux-doc@vger.kernel.org, Heinrich Schuchardt Subject: [PATCH 2/4 v6] kernel/fork.c: avoid division by zero Date: Sun, 15 Mar 2015 17:13:36 +0100 Message-Id: <1426436018-5159-3-git-send-email-xypron.glpk@gmx.de> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1426436018-5159-1-git-send-email-xypron.glpk@gmx.de> References: <1426436018-5159-1-git-send-email-xypron.glpk@gmx.de> X-Provags-ID: V03:K0:BRtXquaZzZd25NwbgWfjRwtdURn3wbCKzejaFQbOlmv5U12pDff jkZO85KecLQhePKYfitN6GLR8keaPOjQDGnB8OPJfXD5cDtKNg5YtK8zETyDSvGQduf9pu/ CV8d4QVMJg/hECGdJ+eFQGyKzHceJJbKv4v4+3SnYbMsY0v1Q88zS0J82FDHU0aR6/aH0cc BQ8/N0gQFll6My+jhWeIw== X-UI-Out-Filterresults: notjunk:1; Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org PAGE_SIZE is not guaranteed to be equal to or less than 8 times the THREAD_SIZE. E.g. architecture hexagon may have page size 1M and thread size 4096. This would lead to a division by zero in the calculation of max_threads. With 32-bit calculation there is no solution which delivers valid results for all possible combinations of the parameters. The code is only called once. Hence a 64-bit calculation can be used as solution. Signed-off-by: Heinrich Schuchardt --- kernel/fork.c | 35 ++++++++++++++++++++++++++--------- 1 file changed, 26 insertions(+), 9 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index bf1ff00..69ff08f 100644 --- a/kernel/fork.c +++ b/kernel/fork.c @@ -88,6 +88,16 @@ #include /* + * Minimum number of threads to boot the kernel + */ +#define MIN_THREADS 20 + +/* + * Maximum number of threads + */ +#define MAX_THREADS FUTEX_TID_MASK + +/* * Protected counters by write_lock_irq(&tasklist_lock) */ unsigned long total_forks; /* Handle normal Linux uptimes. */ @@ -258,18 +268,25 @@ void __init __weak arch_task_cache_init(void) { } */ static void set_max_threads(void) { - /* - * The default maximum number of threads is set to a safe - * value: the thread structures can take up at most half - * of memory. - */ - max_threads = totalram_pages / (8 * THREAD_SIZE / PAGE_SIZE); + u64 threads; /* - * we need to allow at least 20 threads to boot a system + * The number of threads shall be limited such that the thread + * structures may only consume a small part of the available memory. */ - if (max_threads < 20) - max_threads = 20; + if (fls64(totalram_pages) + fls64(PAGE_SIZE) > 64) + threads = MAX_THREADS; + else + threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE, + (u64) THREAD_SIZE * 8UL); + + if (threads > MAX_THREADS) + threads = MAX_THREADS; + + if (threads < MIN_THREADS) + threads = MIN_THREADS; + + max_threads = (int) threads; } void __init fork_init(void) -- 2.1.4