Merge: tracing/osnoise: Allow arbitrarily long CPU string

MR: https://gitlab.com/redhat/centos-stream/src/kernel/centos-stream-10/-/merge_requests/983

# Merge Request Required Information

JIRA: https://issues.redhat.com/browse/RHEL-86520

## Summary of Changes

This improves the osnoise tracer option to handle arbitrarily long CPU strings. Before, it was limited to 256 characters, which was not enough for modern machines with lots of cores.

## Approved Development Ticket(s)
All submissions to CentOS Stream must reference a ticket in [Red Hat Jira](https://issues.redhat.com/).

<details><summary>Click for formatting instructions</summary>
Please follow the CentOS Stream [contribution documentation](https://docs.centos.org/en-US/stream-contrib/quickstart/) for how to file this ticket and have it approved.

List tickets each on their own line of this description using the format "Resolves: RHEL-76229", "Related: RHEL-76229" or "Reverts: RHEL-76229", as appropriate.
</details>

Signed-off-by: Tomas Glozar <tglozar@redhat.com>

Approved-by: Luis Claudio R. Goncalves <lgoncalv@redhat.com>
Approved-by: Gabriele Monaco <gmonaco@redhat.com>
Approved-by: CKI KWF Bot <cki-ci-bot+kwf-gitlab-com@redhat.com>

Merged-by: Julio Faracco <jfaracco@redhat.com>

Author: jcfaracco

kernel/trace/trace_osnoise.c

@@ -2315,7 +2315,7 @@ osnoise_cpus_read(struct file *filp, char __user *ubuf, size_t count,
  * osnoise_cpus_write - Write function for "cpus" entry
  * @filp: The active open file structure
  * @ubuf: The user buffer that contains the value to write
- * @cnt: The maximum number of bytes to write to "file"
+ * @count: The maximum number of bytes to write to "file"
  * @ppos: The current position in @file
  *
  * This function provides a write implementation for the "cpus"
@@ -2333,10 +2333,11 @@ osnoise_cpus_write(struct file *filp, const char __user *ubuf, size_t count,
 {
 	cpumask_var_t osnoise_cpumask_new;
 	int running, err;
-	char buf[256];
+	char *buf __free(kfree) = NULL;
 
-	if (count >= 256)
-		return -EINVAL;
+	buf = kmalloc(count, GFP_KERNEL);
+	if (!buf)
+		return -ENOMEM;
 
 	if (copy_from_user(buf, ubuf, count))
 		return -EFAULT;