Re: bio linked list corruption.

[Chris Mason]

On Tue, Oct 18, 2016 at 05:10:56PM -0700, Linus Torvalds wrote:
> On Tue, Oct 18, 2016 at 4:42 PM, Chris Mason <clm@xxxxxx> wrote:
> > Seems to be the whole thing:
>
> Ahh. On lkml, so I do have it in my mailbox, but Dave changed the
> subject line when he tested on ext4 rather than btrfs..
>
> Anyway, the corrupted address is somewhat interesting. As Dave Jones
> said, he saw
>
>  list_add corruption. prev->next should be next (ffffe8ffff806648),
> but was ffffc9000067fcd8. (prev=ffff880503878b80).
>  list_add corruption. prev->next should be next (ffffe8ffffc05648),
> but was ffffc9000028bcd8. (prev=ffff880503a145c0).
>
> and Dave Chinner reports
>
>  list_add corruption. prev->next should be next (ffffe8ffffc02808),
> but was ffffc90005f6bda8. (prev=ffff88013363bb80).
>
> and it's worth noting that the "but was" is a remarkably consistent
> vmalloc address (the ffffc9000.. pattern gives it away). In fact, it's
> identical across two boots for DaveJ in the low 14 bits, and fairly
> high up in those low 14 bots (0x3cd8).
>
> DaveC has a different address, but it's also in the vmalloc space, and
> also looks like it is fairly high up in 14 bits (0x3da8). So in both
> cases it's almost certainly a stack address with a fairly empty stack.
> The differences are presumably due to different kernel configurations
> and/or just different filesystems calling the same function that does
> the same bad thing but now at different depths in the stack.
>
> Adding Andy to the cc, because this *might* be triggered by the
> vmalloc stack code itself. Maybe the re-use of stacks showing some
> problem? Maybe Chris (who can't see the problem) doesn't have
> CONFIG_VMAP_STACK enabled?

CONFIG_VMAP_STACK=y, but maybe I just need to hammer on process creation 
more.  I'm testing in a hugely stripped down VM, so Dave might have more 
background stuff going on.

-chris