Re: [PATCH] powerpc/nvram: Add spinlock to oops_to_nvram to prevent oops in compression code.

[Jim Keniston <jkenisto@linux.vnet.ibm.com>]

On Thu, 2011-12-01 at 12:46 +1100, Anton Blanchard wrote:
> When issuing a system reset we almost always oops in the oops_to_nvram
> code because multiple CPUs are using the deflate work area. Add a
> spinlock to protect it.
> 
> To play it safe I'm using trylock to avoid locking up if the NVRAM
> code oopses. This means we might miss multiple CPUs oopsing at exactly
> the same time but I think it's best to play it safe for now. Once we
> are happy with the reliability we can change it to a full spinlock.
> 
> Signed-off-by: Anton Blanchard <anton@samba.org>

Acked-by: Jim Keniston <jkenisto@us.ibm.com>

> ---
> 
> Index: linux-build/arch/powerpc/platforms/pseries/nvram.c
> ===================================================================
> --- linux-build.orig/arch/powerpc/platforms/pseries/nvram.c	2011-12-01 09:44:27.205568463 +1100
> +++ linux-build/arch/powerpc/platforms/pseries/nvram.c	2011-12-01 12:36:49.334478156 +1100
> @@ -634,6 +634,8 @@ static void oops_to_nvram(struct kmsg_du
>  {
>  	static unsigned int oops_count = 0;
>  	static bool panicking = false;
> +	static DEFINE_SPINLOCK(lock);
> +	unsigned long flags;
>  	size_t text_len;
>  	unsigned int err_type = ERR_TYPE_KERNEL_PANIC_GZ;
>  	int rc = -1;
> @@ -664,6 +666,9 @@ static void oops_to_nvram(struct kmsg_du
>  	if (clobbering_unread_rtas_event())
>  		return;
> 
> +	if (!spin_trylock_irqsave(&lock, flags))
> +		return;
> +
>  	if (big_oops_buf) {
>  		text_len = capture_last_msgs(old_msgs, old_len,
>  			new_msgs, new_len, big_oops_buf, big_oops_buf_sz);
> @@ -679,4 +684,6 @@ static void oops_to_nvram(struct kmsg_du
> 
>  	(void) nvram_write_os_partition(&oops_log_partition, oops_buf,
>  		(int) (sizeof(*oops_len) + *oops_len), err_type, ++oops_count);
> +
> +	spin_unlock_irqrestore(&lock, flags);
>  }
>