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Date: Sat, 21 Feb 2015 23:19:04 +0100 From: Heinrich Schuchardt <xypron.glpk@....de> To: Andrew Morton <akpm@...ux-foundation.org> Cc: Joe Perches <joe@...ches.com>, Peter Zijlstra <peterz@...radead.org>, Oleg Nesterov <oleg@...hat.com>, Ingo Molnar <mingo@...nel.org>, Vladimir Davydov <vdavydov@...allels.com>, Thomas Gleixner <tglx@...utronix.de>, Kees Cook <keescook@...omium.org>, David Rientjes <rientjes@...gle.com>, Johannes Weiner <hannes@...xchg.org>, "David S. Miller" <davem@...emloft.net>, Andy Lutomirski <luto@...capital.net>, Michael Marineau <mike@...ineau.org>, Aaron Tomlin <atomlin@...hat.com>, Prarit Bhargava <prarit@...hat.com>, Steven Rostedt <rostedt@...dmis.org>, Jens Axboe <axboe@...com>, "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>, Rik van Riel <riel@...hat.com>, Davidlohr Bueso <dave@...olabs.net>, Guenter Roeck <linux@...ck-us.net>, linux-kernel@...r.kernel.org, Heinrich Schuchardt <xypron.glpk@....de> Subject: [PATCH 1/3 v3] kernel/fork.c: avoid division by zero 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 <xypron.glpk@....de> --- 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 <trace/events/task.h> /* + * 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@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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