[PATCH v4] fs/pstore: provide panic data even in suspend

[PATCH v4] fs/pstore: provide panic data even in suspend

[check.kernel]

From: Dongdong Yang <yangdongdong@xiaomi.com>

If system restart after panic, this patch also enables
panic and oops messages which in suspend context to be
logged into ramoops console buffer where it can be read
back at some later point.

Signed-off-by: Dongdong Yang <yangdongdong@xiaomi.com>
Signed-off-by: Linghua Gu <gulinghua@xiaomi.com>
Signed-off-by: Hui Du <duhui@xiaomi.com>
---
 fs/pstore/ram.c        | 16 ++++++++++++++++
 include/linux/printk.h |  6 ++++++
 kernel/printk/printk.c |  6 ++++++
 3 files changed, 28 insertions(+)

diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
index 6c26c4d..3d981a1 100644
--- a/fs/pstore/ram.c
+++ b/fs/pstore/ram.c
@@ -642,8 +642,23 @@ static void ramoops_register_dummy(void)
 	}
 }
 
+static int ramoops_console_notify(struct notifier_block *this,
+		unsigned long event, void *ptr)
+{
+	pr_emerg("ramoops unlock console ...\n");
+	emergency_unlock_console();
+
+	return 0;
+}
+
+static struct notifier_block ramoop_nb = {
+	.notifier_call = ramoops_console_notify,
+	.priority = INT_MAX,
+};
+
 static int __init ramoops_init(void)
 {
+	atomic_notifier_chain_register(&panic_notifier_list, &ramoop_nb);
 	ramoops_register_dummy();
 	return platform_driver_register(&ramoops_driver);
 }
@@ -654,6 +669,7 @@ static void __exit ramoops_exit(void)
 	platform_driver_unregister(&ramoops_driver);
 	platform_device_unregister(dummy);
 	kfree(dummy_data);
+	atomic_notifier_chain_unregister(&panic_notifier_list, &ramoop_nb);
 }
 module_exit(ramoops_exit);
 
diff --git a/include/linux/printk.h b/include/linux/printk.h
index a6298b2..bd043ed 100644
--- a/include/linux/printk.h
+++ b/include/linux/printk.h
@@ -230,6 +230,12 @@ static inline void show_regs_print_info(const char *log_lvl)
 }
 #endif
 
+/*
+ * Enables printk() before emergency_restart
+ * if we go into suspend states and run into oops.
+ */
+void emergency_unlock_console(void);
+
 extern asmlinkage void dump_stack(void) __cold;
 
 #ifndef pr_fmt
diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
index cf8c242..abb8af4 100644
--- a/kernel/printk/printk.c
+++ b/kernel/printk/printk.c
@@ -2107,6 +2107,12 @@ void resume_console(void)
 	console_unlock();
 }
 
+void emergency_unlock_console(void)
+{
+	if (oops_in_progress && panic_timeout != 0 && console_suspended)
+		resume_console();
+}
+
 /**
  * console_cpu_notify - print deferred console messages after CPU hotplug
  * @self: notifier struct
-- 
2.5.0


v4: 
- Move declaration emergency_unlock_console to printk.h from pstore_ram.h
- Update sign-off information.

Thanks,
Dongdong Yang

Re: [PATCH v4] fs/pstore: provide panic data even in suspend

[Petr Mladek]

On Mon 2015-08-17 16:51:39, check.kernel@gmail.com wrote:
> From: Dongdong Yang <yangdongdong@xiaomi.com>
> 
> If system restart after panic, this patch also enables
> panic and oops messages which in suspend context to be
> logged into ramoops console buffer where it can be read
> back at some later point.
> 
> Signed-off-by: Dongdong Yang <yangdongdong@xiaomi.com>
> Signed-off-by: Linghua Gu <gulinghua@xiaomi.com>
> Signed-off-by: Hui Du <duhui@xiaomi.com>
> ---
>  fs/pstore/ram.c        | 16 ++++++++++++++++
>  include/linux/printk.h |  6 ++++++
>  kernel/printk/printk.c |  6 ++++++
>  3 files changed, 28 insertions(+)
> 
> diff --git a/fs/pstore/ram.c b/fs/pstore/ram.c
> index 6c26c4d..3d981a1 100644
> --- a/fs/pstore/ram.c
> +++ b/fs/pstore/ram.c
> @@ -642,8 +642,23 @@ static void ramoops_register_dummy(void)
>  	}
>  }
>  
> +static int ramoops_console_notify(struct notifier_block *this,
> +		unsigned long event, void *ptr)
> +{
> +	pr_emerg("ramoops unlock console ...\n");
> +	emergency_unlock_console();
> +
> +	return 0;
> +}
> +
> +static struct notifier_block ramoop_nb = {
> +	.notifier_call = ramoops_console_notify,
> +	.priority = INT_MAX,
> +};
> +
>  static int __init ramoops_init(void)
>  {
> +	atomic_notifier_chain_register(&panic_notifier_list, &ramoop_nb);
>  	ramoops_register_dummy();
>  	return platform_driver_register(&ramoops_driver);
>  }
> @@ -654,6 +669,7 @@ static void __exit ramoops_exit(void)
>  	platform_driver_unregister(&ramoops_driver);
>  	platform_device_unregister(dummy);
>  	kfree(dummy_data);
> +	atomic_notifier_chain_unregister(&panic_notifier_list, &ramoop_nb);
>  }
>  module_exit(ramoops_exit);
>  
> diff --git a/include/linux/printk.h b/include/linux/printk.h
> index a6298b2..bd043ed 100644
> --- a/include/linux/printk.h
> +++ b/include/linux/printk.h
> @@ -230,6 +230,12 @@ static inline void show_regs_print_info(const char *log_lvl)
>  }
>  #endif
>  
> +/*
> + * Enables printk() before emergency_restart
> + * if we go into suspend states and run into oops.
> + */
> +void emergency_unlock_console(void);
> +
>  extern asmlinkage void dump_stack(void) __cold;
>  
>  #ifndef pr_fmt
> diff --git a/kernel/printk/printk.c b/kernel/printk/printk.c
> index cf8c242..abb8af4 100644
> --- a/kernel/printk/printk.c
> +++ b/kernel/printk/printk.c
> @@ -2107,6 +2107,12 @@ void resume_console(void)
>  	console_unlock();
>  }
>  
> +void emergency_unlock_console(void)
> +{
> +	if (oops_in_progress && panic_timeout != 0 && console_suspended)
> +		resume_console();

IMHO, you need to put "console_sem" down if you want to test
"console_suspended". And you must keep it down until you resume
the console to avoid a race => we could not call resume_console()
in the current form.

Also I am a bit nervous that this operation is not symmetric
and the console will stay resumed. Please look at bust_spinlocks(),
how this function is used in panic(), and see how the
"oops_in_progress" is handled.

To be honest, I do not understand this code in details enough
and I do not have time to investigate it at the moment.
I just use a common sense to produce this feedback. Others
might give you a better feedback. It is possible that this
should get handled a more generic way and not by a ramoops
specific handler.

BTW: Have you tested this with more consoles attached? I wonder
if other consoles are still usable in this situation and if
they will not block the output to ramoops.

Best Regards,
Petr


> +}
> +
>  /**
>   * console_cpu_notify - print deferred console messages after CPU hotplug
>   * @self: notifier struct
> -- 
> 2.5.0
> 
> 
> v4: 
> - Move declaration emergency_unlock_console to printk.h from pstore_ram.h
> - Update sign-off information.
> 
> Thanks,
> Dongdong Yang