Re: discriminate single bit error hardware failure from slab corruption.

[Avi Kivity <avi@argo.co.il>]

Dave Jones wrote:

> In the case where we detect a single bit has been flipped, we spew
> the usual slab corruption message, which users instantly think
> is a kernel bug.  In a lot of cases, single bit errors are
> down to bad memory, or other hardware failure.
>
> This patch adds an extra line to the slab debug messages in those
> cases, in the hope that users will try memtest before they report a bug.
>
> 000: 6b 6b 6b 6b 6a 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b 6b
> Single bit error detected. Possibly bad RAM. Please run memtest86.
>
> Signed-off-by: Dave Jones <davej@redhat.com>
>
> --- linux-2.6.15/mm/slab.c~	2006-01-09 13:25:17.000000000 -0500
> +++ linux-2.6.15/mm/slab.c	2006-01-09 13:26:01.000000000 -0500
> @@ -1313,8 +1313,11 @@ static void poison_obj(kmem_cache_t *cac
> static void dump_line(char *data, int offset, int limit)
> {
> 	int i;
> +	unsigned char total=0;
> 	printk(KERN_ERR "%03x:", offset);
> 	for (i = 0; i < limit; i++) {
> +		if (data[offset+i] != POISON_FREE)
> +			total += data[offset+i];
>  
how about

        total += hweight8(data[offset+i] ^ POISON_FREE);

> 		printk(" %02x", (unsigned char)data[offset + i]);
> 	}
> 	printk("\n");
> @@ -1019,6 +1023,18 @@ static void dump_line(char *data, int of
> 		}
> 	}
> 	printk("\n");
> +	switch (total) {
> +		case 0x36:
> +		case 0x6a:
> +		case 0x6f:
> +		case 0x81:
> +		case 0xac:
> +		case 0xd3:
> +		case 0xd5:
> +		case 0xea:
> +			printk (KERN_ERR "Single bit error detected. Possibly bad RAM. Please run memtest86.\n");
> +			return;
> +	}
>  
and a

    if (total == 1)
          printk(...);

here? it seems more readable and more correct as well.

> }
> #endif
>
>  


--
Do not meddle in the internals of kernels, for they are subtle and quick to panic.

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