Re: Kernel 2.6.19.2 New RAID 5 Bug (oops when writing Samba -> RAID5)

[Justin Piszcz <jpiszcz@lucidpixels.com>]

On Fri, 26 Jan 2007, Andrew Morton wrote:

> On Wed, 24 Jan 2007 18:37:15 -0500 (EST)
> Justin Piszcz <jpiszcz@lucidpixels.com> wrote:
> 
> > > Without digging too deeply, I'd say you've hit the same bug Sami Farin and
> > > others
> > > have reported starting with 2.6.19: pages mapped with kmap_atomic() become
> > > unmapped
> > > during memcpy() or similar operations.  Try disabling preempt -- that seems to
> > > be the
> > > common factor.
> > > 
> > > 
> > > -
> > > To unsubscribe from this list: send the line "unsubscribe linux-raid" in
> > > the body of a message to majordomo@vger.kernel.org
> > > More majordomo info at  http://vger.kernel.org/majordomo-info.html
> > > 
> > > 
> > 
> > After I run some other tests, I am going to re-run this test and see if it 
> > OOPSes again with PREEMPT off.
> 
> Strange.  The below debug patch might catch it - please run with this
> applied.  
> 
> 
> --- a/arch/i386/mm/highmem.c~kmap_atomic-debugging
> +++ a/arch/i386/mm/highmem.c
> @@ -30,7 +30,43 @@ void *kmap_atomic(struct page *page, enu
>  {
>  	enum fixed_addresses idx;
>  	unsigned long vaddr;
> +	static unsigned warn_count = 10;
>  
> +	if (unlikely(warn_count == 0))
> +		goto skip;
> +
> +	if (unlikely(in_interrupt())) {
> +		if (in_irq()) {
> +			if (type != KM_IRQ0 && type != KM_IRQ1 &&
> +			    type != KM_BIO_SRC_IRQ && type != KM_BIO_DST_IRQ &&
> +			    type != KM_BOUNCE_READ) {
> +				WARN_ON(1);
> +				warn_count--;
> +			}
> +		} else if (!irqs_disabled()) {	/* softirq */
> +			if (type != KM_IRQ0 && type != KM_IRQ1 &&
> +			    type != KM_SOFTIRQ0 && type != KM_SOFTIRQ1 &&
> +			    type != KM_SKB_SUNRPC_DATA &&
> +			    type != KM_SKB_DATA_SOFTIRQ &&
> +			    type != KM_BOUNCE_READ) {
> +				WARN_ON(1);
> +				warn_count--;
> +			}
> +		}
> +	}
> +
> +	if (type == KM_IRQ0 || type == KM_IRQ1 || type == KM_BOUNCE_READ) {
> +		if (!irqs_disabled()) {
> +			WARN_ON(1);
> +			warn_count--;
> +		}
> +	} else if (type == KM_SOFTIRQ0 || type == KM_SOFTIRQ1) {
> +		if (irq_count() == 0 && !irqs_disabled()) {
> +			WARN_ON(1);
> +			warn_count--;
> +		}
> +	}
> +skip:
>  	/* even !CONFIG_PREEMPT needs this, for in_atomic in do_page_fault */
>  	pagefault_disable();
>  	if (!PageHighMem(page))
> _
> 
> 

The RAID5 bug may be hard to trigger, I have only made it happen once so 
far (but only tried it once, don't like locking up the raid :)), I will 
re-run the test after applying this patch.

Justin.
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