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Date:   Wed, 14 Oct 2020 15:51:00 -0700
From:   Linus Torvalds <torvalds@...ux-foundation.org>
To:     "Jason A. Donenfeld" <Jason@...c4.com>
Cc:     Al Viro <viro@...iv.linux.org.uk>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-arch <linux-arch@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH v2 20/20] ppc: propagate the calling conventions change
 down to csum_partial_copy_generic()

On Wed, Oct 14, 2020 at 3:27 PM Jason A. Donenfeld <Jason@...c4.com> wrote:
>
> This patch is causing crashes in WireGuard's CI over at
> https://www.wireguard.com/build-status/ . Apparently sending a simple
> network packet winds up triggering refcount_t's warn-on-saturate code. I

Ouch.

The C parts look fairly straightforward, and I don't see how they
could cause that odd refcount issue.

So I assume it's the low-level asm code conversion that is buggy. And
it's apparently the 32-bit conversion, since your ppc64 status looks
fine.

I think it's this instruction:

        addi    r1,r1,16

that should be removed from the function exit, because Al removed the

-       stwu    r1,-16(r1)

on function entry.

So I think you end up with a corrupt stack pointer and basically
random behavior.

Mind trying that? (This is obviously all in
arch/powerpc/lib/checksum_32.S, the csum_partial_copy_generic()
function).

               Linus

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