Re: 4.0.0-rc4: panic in free_block

[David Ahern <david.ahern@oracle.com>]

On 3/23/15 10:25 AM, David Miller wrote:
> [PATCH] sparc64: Fix several bugs in memmove().
>
> Firstly, handle zero length calls properly.  Believe it or not there
> are a few of these happening during early boot.
>
> Next, we can't just drop to a memcpy() call in the forward copy case
> where dst <= src.  The reason is that the cache initializing stores
> used in the Niagara memcpy() implementations can end up clearing out
> cache lines before we've sourced their original contents completely.
>
> For example, considering NG4memcpy, the main unrolled loop begins like
> this:
>
>       load   src + 0x00
>       load   src + 0x08
>       load   src + 0x10
>       load   src + 0x18
>       load   src + 0x20
>       store  dst + 0x00
>
> Assume dst is 64 byte aligned and let's say that dst is src - 8 for
> this memcpy() call.  That store at the end there is the one to the
> first line in the cache line, thus clearing the whole line, which thus
> clobbers "src + 0x28" before it even gets loaded.
>
> To avoid this, just fall through to a simple copy only mildly
> optimized for the case where src and dst are 8 byte aligned and the
> length is a multiple of 8 as well.  We could get fancy and call
> GENmemcpy() but this is good enough for how this thing is actually
> used.
>
> Reported-by: David Ahern <david.ahern@oracle.com>
> Reported-by: Bob Picco <bpicco@meloft.net>
> Signed-off-by: David S. Miller <davem@davemloft.net>

seems like a formality at this point, but this resolves the panic on the 
M7-based ldom and baremetal. The T5-8 failed to boot, but it could be a 
different problem.

Thanks for the fast turnaround,
David