Re: m68k boot failure in -next bisected to 'xarray: Replace exceptional entries'

[Matthew Wilcox <willy@infradead.org>]

On Fri, Jun 22, 2018 at 11:42:46AM -0700, Guenter Roeck wrote:
> Hi,
> 
> a few days ago, m68k boot tests in linux-next started to crash.
> I bisected the problem to commit 'xarray: Replace exceptional entries'.
> Bisect and crash logs are attached below.

Thank you!  I was afraid something like this might happen.  

> ------------[ cut here ]------------
> WARNING: CPU: 0 PID: 1 at lib/idr.c:42 idr_alloc_u32+0x44/0xe8

Line 42 is:

        if (WARN_ON_ONCE(radix_tree_is_internal_node(ptr)))
                return -EINVAL;

The pointer passed in to idr_alloc() is not 4-byte aligned; it's aligned
to a 2 byte boundary.  I'm having a little trouble seeing who it is that's
passing in what pointer ...

> Call Trace: [<000180d6>] __warn+0xc0/0xc2
>  [<000020e8>] do_one_initcall+0x0/0x140
>  [<0001816a>] warn_slowpath_null+0x26/0x2c
>  [<002b50e4>] idr_alloc_u32+0x44/0xe8
>  [<002b50e4>] idr_alloc_u32+0x44/0xe8
>  [<002b51e4>] idr_alloc+0x5c/0x76
>  [<00247160>] genl_register_family+0x14c/0x54c

It makes sense to here (other than idr_alloc being listed twice)

>  [<000020e8>] do_one_initcall+0x0/0x140
>  [<003f0f02>] genl_init+0x0/0x34

Assuming this is right, that would imply that genl_ctrl is not 4-byte
aligned.  Is that true?  I'm not familiar with the m68k alignment rules,
but it has a lot of 4-byte sized quantities in the struct, so I would
assume it's 4-byte aligned.

>  [<003f0ce6>] bpf_lwt_init+0x10/0x14

I don't think this is the caller.

>  [<003f0f0e>] genl_init+0xc/0x34
>  [<00002142>] do_one_initcall+0x5a/0x140
>  [<00029828>] parse_args+0x0/0x202
>  [<000020e8>] do_one_initcall+0x0/0x140
>  [<002bf6c4>] strcpy+0x0/0x1c
>  [<00040004>] timekeeping_resume+0x280/0x2cc
>  [<003df1e6>] kernel_init_freeable+0x176/0x190
>  [<002bf6c4>] strcpy+0x0/0x1c
>  [<003df1fc>] kernel_init_freeable+0x18c/0x190
>  [<003f0f02>] genl_init+0x0/0x34
>  [<002c4b66>] kernel_init+0x0/0xd2
>  [<002c4b6e>] kernel_init+0x8/0xd2
>  [<002c4b66>] kernel_init+0x0/0xd2
>  [<000028e0>] ret_from_kernel_thread+0xc/0x14
> ---[ end trace 62c263e59debfdfe ]---
> Kernel panic - not syncing: GENL: Cannot register controller: -22