Commit 90e406f9 authored by Changbin Du's avatar Changbin Du Committed by Steven Rostedt (VMware)
Browse files

tracing: Allocate mask_str buffer dynamically 

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: 36dfe925 ("ftrace: make use of tracing_cpumask")
Cc: stable@vger.kernel.org
Signed-off-by: default avatarChangbin Du <changbin.du@intel.com>
Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
parent 250d0c77

kernel/trace/trace.c

+9 −20
Original line number Diff line number Diff line
@@ -4178,37 +4178,30 @@ static const struct file_operations show_traces_fops = { 
	.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;

}
@@ -4228,8 +4221,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf, 
	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) {
@@ -4252,8 +4243,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf, 
	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;

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