1. 29 Jan, 2021 1 commit
    • Steven Rostedt (VMware)'s avatar
      fgraph: Initialize tracing_graph_pause at task creation · 7e0a9220
      Steven Rostedt (VMware) authored
      On some archs, the idle task can call into cpu_suspend(). The cpu_suspend()
      will disable or pause function graph tracing, as there's some paths in
      bringing down the CPU that can have issues with its return address being
      modified. The task_struct structure has a "tracing_graph_pause" atomic
      counter, that when set to something other than zero, the function graph
      tracer will not modify the return address.
      
      The problem is that the tracing_graph_pause counter is initialized when the
      function graph tracer is enabled. This can corrupt the counter for the idle
      task if it is suspended in these architectures.
      
         CPU 1				CPU 2
         -----				-----
        do_idle()
          cpu_suspend()
            pause_graph_tracing()
                task_struct->tracing_graph_pause++ (0 -> 1)
      
      				start_graph_tracing()
      				  for_each_online_cpu(cpu) {
      				    ftrace_graph_init_idle_task(cpu)
      				      task-struct->tracing_graph_pause = 0 (1 -> 0)
      
            unpause_graph_tracing()
                task_struct->tracing_graph_pause-- (0 -> -1)
      
      The above should have gone from 1 to zero, and enabled function graph
      tracing again. But instead, it is set to -1, which keeps it disabled.
      
      There's no reason that the field tracing_graph_pause on the task_struct can
      not be initialized at boot up.
      
      Cc: stable@vger.kernel.org
      Fixes: 380c4b14 ("tracing/function-graph-tracer: append the tracing_graph_flag")
      Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=211339
      Reported-by: pierre.gondois@arm.com
      Signed-off-by: default avatarSteven Rostedt (VMware) <rostedt@goodmis.org>
      7e0a9220
  2. 25 Jan, 2021 1 commit
  3. 24 Jan, 2021 37 commits
  4. 23 Jan, 2021 1 commit