linux-kernel - Re: [PATCH] ledtrig-cpu: kill useless mutex to fix sleep in atomic context

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Message-ID: <CAK5ve-+AYDM7eo1SBkMs-zHwnQL2URXc8zZJPQX9NeHD1DOTNg@mail.gmail.com>
Date:	Mon, 5 Nov 2012 17:06:27 -0800
From:	Bryan Wu <cooloney@...il.com>
To:	Nathan Lynch <ntl@...ox.com>
Cc:	linux-leds@...r.kernel.org, linux-kernel@...r.kernel.org,
	miles.lane@...il.com
Subject: Re: [PATCH] ledtrig-cpu: kill useless mutex to fix sleep in atomic context

On Mon, Nov 5, 2012 at 6:20 AM, Nathan Lynch <ntl@...ox.com> wrote:
> Seeing the following every time the CPU enters or leaves idle on a
> Beagleboard:
>
> BUG: sleeping function called from invalid context at kernel/mutex.c:269
> in_atomic(): 1, irqs_disabled(): 0, pid: 0, name: swapper/0
> no locks held by swapper/0/0.
> [<c001659c>] (unwind_backtrace+0x0/0xf8) from [<c05aaa7c>] (mutex_lock_nested+0x24/0x380)
> [<c05aaa7c>] (mutex_lock_nested+0x24/0x380) from [<c043bd1c>] (ledtrig_cpu+0x38/0x88)
> [<c043bd1c>] (ledtrig_cpu+0x38/0x88) from [<c000f4b0>] (cpu_idle+0xf4/0x120)
> [<c000f4b0>] (cpu_idle+0xf4/0x120) from [<c07e47c8>] (start_kernel+0x2bc/0x30c)
>
> Miles Lane has reported seeing similar splats during system suspend.
>
> The mutex in struct led_trigger_cpu appears to have no function: it
> resides in a per-cpu data structure which never changes after the
> trigger is registered.  So just remove it.
>
> Reported-by: Miles Lane <miles.lane@...il.com>
> Signed-off-by: Nathan Lynch <ntl@...ox.com>

Thanks, I also think we probable don't need this locking for per CPU
data. But if I'm wrong please correct me.

I will merge this and send to Linus soon.

-Bryan

> ---
>  drivers/leds/ledtrig-cpu.c | 21 ---------------------
>  1 file changed, 21 deletions(-)
>
> diff --git a/drivers/leds/ledtrig-cpu.c b/drivers/leds/ledtrig-cpu.c
> index b312056..4239b39 100644
> --- a/drivers/leds/ledtrig-cpu.c
> +++ b/drivers/leds/ledtrig-cpu.c
> @@ -33,8 +33,6 @@
>  struct led_trigger_cpu {
>         char name[MAX_NAME_LEN];
>         struct led_trigger *_trig;
> -       struct mutex lock;
> -       int lock_is_inited;
>  };
>
>  static DEFINE_PER_CPU(struct led_trigger_cpu, cpu_trig);
> @@ -50,12 +48,6 @@ void ledtrig_cpu(enum cpu_led_event ledevt)
>  {
>         struct led_trigger_cpu *trig = &__get_cpu_var(cpu_trig);
>
> -       /* mutex lock should be initialized before calling mutex_call() */
> -       if (!trig->lock_is_inited)
> -               return;
> -
> -       mutex_lock(&trig->lock);
> -
>         /* Locate the correct CPU LED */
>         switch (ledevt) {
>         case CPU_LED_IDLE_END:
> @@ -75,8 +67,6 @@ void ledtrig_cpu(enum cpu_led_event ledevt)
>                 /* Will leave the LED as it is */
>                 break;
>         }
> -
> -       mutex_unlock(&trig->lock);
>  }
>  EXPORT_SYMBOL(ledtrig_cpu);
>
> @@ -117,14 +107,9 @@ static int __init ledtrig_cpu_init(void)
>         for_each_possible_cpu(cpu) {
>                 struct led_trigger_cpu *trig = &per_cpu(cpu_trig, cpu);
>
> -               mutex_init(&trig->lock);
> -
>                 snprintf(trig->name, MAX_NAME_LEN, "cpu%d", cpu);
>
> -               mutex_lock(&trig->lock);
>                 led_trigger_register_simple(trig->name, &trig->_trig);
> -               trig->lock_is_inited = 1;
> -               mutex_unlock(&trig->lock);
>         }
>
>         register_syscore_ops(&ledtrig_cpu_syscore_ops);
> @@ -142,15 +127,9 @@ static void __exit ledtrig_cpu_exit(void)
>         for_each_possible_cpu(cpu) {
>                 struct led_trigger_cpu *trig = &per_cpu(cpu_trig, cpu);
>
> -               mutex_lock(&trig->lock);
> -
>                 led_trigger_unregister_simple(trig->_trig);
>                 trig->_trig = NULL;
>                 memset(trig->name, 0, MAX_NAME_LEN);
> -               trig->lock_is_inited = 0;
> -
> -               mutex_unlock(&trig->lock);
> -               mutex_destroy(&trig->lock);
>         }
>
>         unregister_syscore_ops(&ledtrig_cpu_syscore_ops);
> --
> 1.7.11.7
>
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