tracing: Allocate mask_str buffer dynamically
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 <changbin.du@intel.com> Signed-off-by: Steven Rostedt (VMware) <rostedt@goodmis.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
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@ -4178,37 +4178,30 @@ static const struct file_operations show_traces_fops = {
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.llseek = seq_lseek,
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};
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/*
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* The tracer itself will not take this lock, but still we want
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* to provide a consistent cpumask to user-space:
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*/
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static DEFINE_MUTEX(tracing_cpumask_update_lock);
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/*
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* Temporary storage for the character representation of the
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* CPU bitmask (and one more byte for the newline):
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*/
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static char mask_str[NR_CPUS + 1];
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static ssize_t
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tracing_cpumask_read(struct file *filp, char __user *ubuf,
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size_t count, loff_t *ppos)
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{
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struct trace_array *tr = file_inode(filp)->i_private;
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char *mask_str;
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int len;
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mutex_lock(&tracing_cpumask_update_lock);
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len = snprintf(NULL, 0, "%*pb\n",
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cpumask_pr_args(tr->tracing_cpumask)) + 1;
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mask_str = kmalloc(len, GFP_KERNEL);
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if (!mask_str)
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return -ENOMEM;
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len = snprintf(mask_str, count, "%*pb\n",
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len = snprintf(mask_str, len, "%*pb\n",
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cpumask_pr_args(tr->tracing_cpumask));
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if (len >= count) {
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count = -EINVAL;
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goto out_err;
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}
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count = simple_read_from_buffer(ubuf, count, ppos, mask_str, NR_CPUS+1);
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count = simple_read_from_buffer(ubuf, count, ppos, mask_str, len);
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out_err:
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mutex_unlock(&tracing_cpumask_update_lock);
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kfree(mask_str);
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return count;
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}
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@ -4228,8 +4221,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
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if (err)
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goto err_unlock;
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mutex_lock(&tracing_cpumask_update_lock);
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local_irq_disable();
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arch_spin_lock(&tr->max_lock);
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for_each_tracing_cpu(cpu) {
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@ -4252,8 +4243,6 @@ tracing_cpumask_write(struct file *filp, const char __user *ubuf,
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local_irq_enable();
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cpumask_copy(tr->tracing_cpumask, tracing_cpumask_new);
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mutex_unlock(&tracing_cpumask_update_lock);
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free_cpumask_var(tracing_cpumask_new);
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return count;
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