Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752179AbbBUWUp (ORCPT ); Sat, 21 Feb 2015 17:20:45 -0500 Received: from mout.gmx.net ([212.227.17.22]:57012 "EHLO mout.gmx.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752082AbbBUWUm (ORCPT ); Sat, 21 Feb 2015 17:20:42 -0500 From: Heinrich Schuchardt To: Andrew Morton Cc: Joe Perches , Peter Zijlstra , Oleg Nesterov , Ingo Molnar , Vladimir Davydov , Thomas Gleixner , Kees Cook , David Rientjes , Johannes Weiner , "David S. Miller" , Andy Lutomirski , Michael Marineau , Aaron Tomlin , Prarit Bhargava , Steven Rostedt , Jens Axboe , "Paul E. McKenney" , Rik van Riel , Davidlohr Bueso , Guenter Roeck , linux-kernel@vger.kernel.org, Heinrich Schuchardt Subject: [PATCH 1/3 v3] kernel/fork.c: avoid division by zero Date: Sat, 21 Feb 2015 23:19:04 +0100 Message-Id: <1424557146-29965-2-git-send-email-xypron.glpk@gmx.de> X-Mailer: git-send-email 2.1.4 In-Reply-To: <1424557146-29965-1-git-send-email-xypron.glpk@gmx.de> References: <20150218122851.d1ae723ff12887f9ab919431@linux-foundation.org> <1424557146-29965-1-git-send-email-xypron.glpk@gmx.de> X-Provags-ID: V03:K0:vRIZ90lmJdb5VOq3qlVwWP4K0FZu+zGfCg7pJx2XoRzpqVX6JDB fPshWw83oFWivDSORZ42tcrGllKkwfkxsBxJthiHiBqi1LLhblxyaVfU8Di86cN/LJYSseI BN8YnGCvZIpAA3XV/B89dbf6kfKAURbbVujHqrfuwwOWOOX/EBNoObfBFwIjeY+qlgNIjKi c8x4ZZH0KFb95DCuQqI4g== 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: 3402 Lines: 113 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 | 59 ++++++++++++++++++++++++++++++++++++++++++----------------- 1 file changed, 42 insertions(+), 17 deletions(-) diff --git a/kernel/fork.c b/kernel/fork.c index 4dc2dda..69c30cd 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. */ @@ -253,6 +263,37 @@ EXPORT_SYMBOL_GPL(__put_task_struct); void __init __weak arch_task_cache_init(void) { } +/* + * set_max_threads tries to set default limit to the suggested value. + */ +static void set_max_threads(unsigned int max_threads_suggested) +{ + u64 threads; + + /* + * The number of threads shall be limited such that the thread + * structures may only consume a small part of the available memory. + */ + 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 = (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]; +} + void __init fork_init(unsigned long mempages) { #ifndef CONFIG_ARCH_TASK_STRUCT_ALLOCATOR @@ -268,23 +309,7 @@ void __init fork_init(unsigned long mempages) /* do the arch specific task caches init */ arch_task_cache_init(); - /* - * 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 = mempages / (8 * THREAD_SIZE / PAGE_SIZE); - - /* - * we need to allow at least 20 threads to boot a system - */ - if (max_threads < 20) - max_threads = 20; - - 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_SIGPENDING] = - init_task.signal->rlim[RLIMIT_NPROC]; + set_max_threads(UINT_MAX); } int __weak arch_dup_task_struct(struct task_struct *dst, -- 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/