[PATCH] powerpc/pseries: Stop calling printk in rtas_stop_self()

[PATCH] powerpc/pseries: Stop calling printk in rtas_stop_self()

[Michael Ellerman]

RCU complains about us calling printk() from an offline CPU:

  =============================
  WARNING: suspicious RCU usage
  5.12.0-rc7-02874-g7cf90e481cb8 #1 Not tainted
  -----------------------------
  kernel/locking/lockdep.c:3568 RCU-list traversed in non-reader section!!

  other info that might help us debug this:

  RCU used illegally from offline CPU!
  rcu_scheduler_active = 2, debug_locks = 1
  no locks held by swapper/0/0.

  stack backtrace:
  CPU: 0 PID: 0 Comm: swapper/0 Not tainted 5.12.0-rc7-02874-g7cf90e481cb8 #1
  Call Trace:
    dump_stack+0xec/0x144 (unreliable)
    lockdep_rcu_suspicious+0x124/0x144
    __lock_acquire+0x1098/0x28b0
    lock_acquire+0x128/0x600
    _raw_spin_lock_irqsave+0x6c/0xc0
    down_trylock+0x2c/0x70
    __down_trylock_console_sem+0x60/0x140
    vprintk_emit+0x1a8/0x4b0
    vprintk_func+0xcc/0x200
    printk+0x40/0x54
    pseries_cpu_offline_self+0xc0/0x120
    arch_cpu_idle_dead+0x54/0x70
    do_idle+0x174/0x4a0
    cpu_startup_entry+0x38/0x40
    rest_init+0x268/0x388
    start_kernel+0x748/0x790
    start_here_common+0x1c/0x614

Which happens because by the time we get to rtas_stop_self() we are
already offline. In addition the message can be spammy, and is not that
helpful for users, so remove it.

Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
---
 arch/powerpc/platforms/pseries/hotplug-cpu.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/arch/powerpc/platforms/pseries/hotplug-cpu.c b/arch/powerpc/platforms/pseries/hotplug-cpu.c
index ec478f8a98ff..48d9dfc3fad1 100644
--- a/arch/powerpc/platforms/pseries/hotplug-cpu.c
+++ b/arch/powerpc/platforms/pseries/hotplug-cpu.c
@@ -47,9 +47,6 @@ static void rtas_stop_self(void)
 
 	BUG_ON(rtas_stop_self_token == RTAS_UNKNOWN_SERVICE);
 
-	printk("cpu %u (hwid %u) Ready to die...\n",
-	       smp_processor_id(), hard_smp_processor_id());
-
 	rtas_call_unlocked(&args, rtas_stop_self_token, 0, 1, NULL);
 
 	panic("Alas, I survived.\n");
-- 
2.25.1

Re: [PATCH] powerpc/pseries: Stop calling printk in rtas_stop_self()

[Michael Ellerman]

On Sun, 18 Apr 2021 23:54:13 +1000, Michael Ellerman wrote:
> RCU complains about us calling printk() from an offline CPU:
> 
>   =============================
>   WARNING: suspicious RCU usage
>   5.12.0-rc7-02874-g7cf90e481cb8 #1 Not tainted
>   -----------------------------
>   kernel/locking/lockdep.c:3568 RCU-list traversed in non-reader section!!
> 
> [...]

Applied to powerpc/next.

[1/1] powerpc/pseries: Stop calling printk in rtas_stop_self()
      https://git.kernel.org/powerpc/c/ed8029d7b472369a010a1901358567ca3b6dbb0d

cheers