Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752825AbbBWUQk (ORCPT ); Mon, 23 Feb 2015 15:16:40 -0500 Received: from mout.gmx.net ([212.227.15.19]:55284 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752716AbbBWUQh (ORCPT ); Mon, 23 Feb 2015 15:16:37 -0500 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 , 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, Heinrich Schuchardt Subject: [PATCH 2/4 v4] kernel/fork.c: avoid division by zero Date: Mon, 23 Feb 2015 21:14:35 +0100 Message-Id: <1424722477-23758-3-git-send-email-xypron.glpk@gmx.de> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1424722477-23758-1-git-send-email-xypron.glpk@gmx.de> References: <20150222075825.GA20626@gmail.com> <1424722477-23758-1-git-send-email-xypron.glpk@gmx.de> X-Provags-ID: V03:K0:zF/bK9N+veWXJng+2KjkA3y9Q0YZTLqYre7M75OkRqKM29PoPg4 KYkMRZZ0h9IA2xW+pNVBOT5I34/XM4i6qLUZ5Q2D430Nw+1PSSpU6lsMFyjY68uCfVSo3KM lCesCQ/sCIQz1pU/2Jx9FGBMchgCT/I6jX4KFdikkxUTw0/mi+LwJEaYHPd7IRTHJZAFjyW x40Xmb/9j60NrwkAOLA9Q== X-UI-Out-Filterresults: notjunk:1; Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 3013 Lines: 96 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 calculus 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. The calculation of max_threads is moved to a separate function. This allows future patches to use the same logic, e.g. when - max_threads is set by writing to /proc/sys/kernel/threads-max - when adding or removing memory. Signed-off-by: Heinrich Schuchardt --- kernel/fork.c | 42 +++++++++++++++++++++++++++++------------- 1 file changed, 29 insertions(+), 13 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 3a423b2..4d68e1e 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. */ @@ -254,26 +264,32 @@ EXPORT_SYMBOL_GPL(__put_task_struct); void __init __weak arch_task_cache_init(void) { } /* - * set_max_threads - * The argument is ignored. + * set_max_threads tries to set the default limit to the suggested value. */ static void set_max_threads(unsigned int max_threads_suggested) { - /* - * 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; + threads = div64_u64((u64) totalram_pages * (u64) PAGE_SIZE, + (u64) THREAD_SIZE * 8UL); + + if (threads > max_threads_suggested) + threads = max_threads_suggested; + + if (threads > MAX_THREADS) + threads = MAX_THREADS; + + if (threads < MIN_THREADS) + threads = MIN_THREADS; + + max_threads = (int) threads; - init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = max_threads/2; - init_task.signal->rlim[RLIMIT_NPROC].rlim_max = max_threads/2; + init_task.signal->rlim[RLIMIT_NPROC].rlim_cur = (int) threads / 2; + init_task.signal->rlim[RLIMIT_NPROC].rlim_max = (int) threads / 2; init_task.signal->rlim[RLIMIT_SIGPENDING] = init_task.signal->rlim[RLIMIT_NPROC]; } -- 2.1.4 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/