From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934552AbdLRP7Z (ORCPT ); Mon, 18 Dec 2017 10:59:25 -0500 Received: from mail.linuxfoundation.org ([140.211.169.12]:37300 "EHLO mail.linuxfoundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934785AbdLRP7R (ORCPT ); Mon, 18 Dec 2017 10:59:17 -0500 From: Greg Kroah-Hartman To: linux-kernel@vger.kernel.org Cc: Greg Kroah-Hartman , stable@vger.kernel.org, Changbin Du , "Steven Rostedt (VMware)" Subject: [PATCH 4.9 006/177] tracing: Allocate mask_str buffer dynamically Date: Mon, 18 Dec 2017 16:47:09 +0100 Message-Id: <20171218152910.167128573@linuxfoundation.org> X-Mailer: git-send-email 2.15.1 In-Reply-To: <20171218152909.823644066@linuxfoundation.org> References: <20171218152909.823644066@linuxfoundation.org> User-Agent: quilt/0.65 MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 4.9-stable review patch. If anyone has any objections, please let me know. ------------------ From: Changbin Du commit 90e406f96f630c07d631a021fd4af10aac913e77 upstream. The default NR_CPUS can be very large, but actual possible nr_cpu_ids usually is very small. For my x86 distribution, the NR_CPUS is 8192 and nr_cpu_ids is 4. About 2 pages are wasted. Most machines don't have so many CPUs, so define a array with NR_CPUS just wastes memory. So let's allocate the buffer dynamically when need. With this change, the mutext tracing_cpumask_update_lock also can be removed now, which was used to protect mask_str. Link: http://lkml.kernel.org/r/1512013183-19107-1-git-send-email-changbin.du@intel.com Fixes: 36dfe9252bd4c ("ftrace: make use of tracing_cpumask") Signed-off-by: Changbin Du Signed-off-by: Steven Rostedt (VMware) Signed-off-by: Greg Kroah-Hartman --- kernel/trace/trace.c | 29 +++++++++-------------------- 1 file changed, 9 insertions(+), 20 deletions(-) --- a/kernel/trace/trace.c +++ b/kernel/trace/trace.c @@ -3727,37 +3727,30 @@ static const struct file_operations show .llseek = seq_lseek, }; -/* - * The tracer itself will not take this lock, but still we want - * to provide a consistent cpumask to user-space: - */ -static DEFINE_MUTEX(tracing_cpumask_update_lock); - -/* - * Temporary storage for the character representation of the - * CPU bitmask (and one more byte for the newline): - */ -static char mask_str[NR_CPUS + 1]; - static ssize_t tracing_cpumask_read(struct file *filp, char __user *ubuf, size_t count, loff_t *ppos) { struct trace_array *tr = file_inode(filp)->i_private; + char *mask_str; int len; - mutex_lock(&tracing_cpumask_update_lock); + len = snprintf(NULL, 0, "%*pb\n", + cpumask_pr_args(tr->tracing_cpumask)) + 1; + mask_str = kmalloc(len, GFP_KERNEL); + if (!mask_str) + return -ENOMEM; - len = snprintf(mask_str, count, "%*pb\n", + len = snprintf(mask_str, len, "%*pb\n", cpumask_pr_args(tr->tracing_cpumask)); if (len >= count) { count = -EINVAL; goto out_err; } - count = simple_read_from_buffer(ubuf, count, ppos, mask_str, NR_CPUS+1); + count = simple_read_from_buffer(ubuf, count, ppos, mask_str, len); out_err: - mutex_unlock(&tracing_cpumask_update_lock); + kfree(mask_str); return count; } @@ -3777,8 +3770,6 @@ tracing_cpumask_write(struct file *filp, if (err) goto err_unlock; - mutex_lock(&tracing_cpumask_update_lock); - local_irq_disable(); arch_spin_lock(&tr->max_lock); for_each_tracing_cpu(cpu) { @@ -3801,8 +3792,6 @@ tracing_cpumask_write(struct file *filp, local_irq_enable(); cpumask_copy(tr->tracing_cpumask, tracing_cpumask_new); - - mutex_unlock(&tracing_cpumask_update_lock); free_cpumask_var(tracing_cpumask_new); return count;