kernel/hung_task.c: force console verbose before panic

Based on commit 401c636a0eeb ("kernel/hung_task.c: show all hung tasks
before panic"), we could get the call stack of hung task.

However, if the console loglevel is not high, we still can not see the
useful panic information in practice, and in most cases users don't set
console loglevel to high level.

This patch is to force console verbose before system panic, so that the
real useful information can be seen in the console, instead of being
like the following, which doesn't have hung task information.

  INFO: task init:1 blocked for more than 120 seconds.
        Tainted: G     U  W         4.19.0-quilt-2e5dc0ac-g51b6c21d76cc #1
  "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
  Kernel panic - not syncing: hung_task: blocked tasks
  CPU: 2 PID: 479 Comm: khungtaskd Tainted: G     U  W         4.19.0-quilt-2e5dc0ac-g51b6c21d76cc #1
  Call Trace:
   dump_stack+0x4f/0x65
   panic+0xde/0x231
   watchdog+0x290/0x410
   kthread+0x12c/0x150
   ret_from_fork+0x35/0x40
  reboot: panic mode set: p,w
  Kernel Offset: 0x34000000 from 0xffffffff81000000 (relocation range: 0xffffffff80000000-0xffffffffbfffffff)

Link: http://lkml.kernel.org/r/27240C0AC20F114CBF8149A2696CBE4A6015B675@SHSMSX101.ccr.corp.intel.com
Signed-off-by: Chuansheng Liu <chuansheng.liu@intel.com>
Reviewed-by: Petr Mladek <pmladek@suse.com>
Reviewed-by: Sergey Senozhatsky <sergey.senozhatsky@gmail.com>
Cc: Tetsuo Handa <penguin-kernel@i-love.sakura.ne.jp>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

diff --git a/kernel/hung_task.c b/kernel/hung_task.c
index cb8e3e8ac7b90b14b2bb0dd97dcdc7c5d02c3afe..85af0cde7f46a4fd6e992439b7383d16721cdf18 100644 (file)
--- a/kernel/hung_task.c
+++ b/kernel/hung_task.c
@@ -112,8 +112,11 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
 
        trace_sched_process_hang(t);
 
-       if (!sysctl_hung_task_warnings && !sysctl_hung_task_panic)
-               return;
+       if (sysctl_hung_task_panic) {
+               console_verbose();
+               hung_task_show_lock = true;
+               hung_task_call_panic = true;
+       }
 
        /*
         * Ok, the task did not get scheduled for more than 2 minutes,
@@ -135,11 +138,6 @@ static void check_hung_task(struct task_struct *t, unsigned long timeout)
        }
 
        touch_nmi_watchdog();
-
-       if (sysctl_hung_task_panic) {
-               hung_task_show_lock = true;
-               hung_task_call_panic = true;
-       }
 }
 
 /*