tracing/osnoise: Fix possible recursive locking for cpus_read_lock()

JIRA: https://issues.redhat.com/browse/RHEL-117873

commit 7e6b3fc
Author: Ran Xiaokai <ran.xiaokai@zte.com.cn>
Date:   Fri Mar 21 09:52:49 2025 +0000

    tracing/osnoise: Fix possible recursive locking for cpus_read_lock()

    Lockdep reports this deadlock log:

    osnoise: could not start sampling thread
    ============================================
    WARNING: possible recursive locking detected
    --------------------------------------------
           CPU0
           ----
      lock(cpu_hotplug_lock);
      lock(cpu_hotplug_lock);

     Call Trace:
      <TASK>
      print_deadlock_bug+0x282/0x3c0
      __lock_acquire+0x1610/0x29a0
      lock_acquire+0xcb/0x2d0
      cpus_read_lock+0x49/0x120
      stop_per_cpu_kthreads+0x7/0x60
      start_kthread+0x103/0x120
      osnoise_hotplug_workfn+0x5e/0x90
      process_one_work+0x44f/0xb30
      worker_thread+0x33e/0x5e0
      kthread+0x206/0x3b0
      ret_from_fork+0x31/0x50
      ret_from_fork_asm+0x11/0x20
      </TASK>

    This is the deadlock scenario:
    osnoise_hotplug_workfn()
      guard(cpus_read_lock)();      // first lock call
      start_kthread(cpu)
        if (IS_ERR(kthread)) {
          stop_per_cpu_kthreads(); {
            cpus_read_lock();      // second lock call. Cause the AA deadlock
          }
        }

    It is not necessary to call stop_per_cpu_kthreads() which stops osnoise
    kthread for every other CPUs in the system if a failure occurs during
    hotplug of a certain CPU.
    For start_per_cpu_kthreads(), if the start_kthread() call fails,
    this function calls stop_per_cpu_kthreads() to handle the error.
    Therefore, similarly, there is no need to call stop_per_cpu_kthreads()
    again within start_kthread().
    So just remove stop_per_cpu_kthreads() from start_kthread to solve this issue.

    Cc: stable@vger.kernel.org
    Link: https://lore.kernel.org/20250321095249.2739397-1-ranxiaokai627@163.com
    Fixes: c8895e2 ("trace/osnoise: Support hotplug operations")
    Signed-off-by: Ran Xiaokai <ran.xiaokai@zte.com.cn>
    Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>

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

Author: lenticularis39

kernel/trace/trace_osnoise.c

@@ -2012,7 +2012,6 @@ static int start_kthread(unsigned int cpu)
 
 	if (IS_ERR(kthread)) {
 		pr_err(BANNER "could not start sampling thread\n");
-		stop_per_cpu_kthreads();
 		return -ENOMEM;
 	}