Re: one time crash in usb_allocmem_flags

[Nick Hudson <skrll%netbsd.org@localhost>]

On 02/09/14 19:48, Alexander Nasonov wrote:
> Hi,
>
> I was running current amd64 (last updated few weeks ago) when I got
> a random crash shortly after switching to X mode. If my analysis is
> correct, it crashed in usb_allocmem_flags inside this loop:
>
>          LIST_FOREACH(f, &usb_frag_freelist, next) {
>                  KDASSERTMSG(usb_valid_block_p(f->block, &usb_blk_fraglist),
>                      "%s: usb frag %p: unknown block pointer %p",
>                       __func__, f, f->block);
>                  if (f->block->tag == tag)
>                          break;
>          }
>
> It couldn't access f->block->tag. I wasn't actively using any of
> the usb devices at that time. I wonder if it's a known problem or
> should I file a PR? Details of the analysis is below.

Please fill a PR so it doesn't get forgotten about.

At first glance it doesn't look like that usb_frag_freelist isn't 
protected correctly. I looks more like random corruption. What was the 
value of %edx?

Thanks,
Nick