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SubjectRe: m68k boot failure in -next bisected to 'xarray: Replace exceptional entries'
On Fri, Jun 22, 2018 at 02:05:19PM -0700, Matthew Wilcox wrote:
> 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.
>

Here is the culprit:

genl_register_family(0x36dd7a) registering VFS_DQUOT
------------[ cut here ]------------
WARNING: CPU: 0 PID: 1 at lib/idr.c:42 idr_alloc_u32+0x44/0xe8

It may be odd that fs/quota/netlink.c:quota_genl_family is not word
aligned, but on the other side I don't think there is a rule that
the function parameter to genl_register_family() - or the second
parameter of idr_alloc() - must be word aligned. Am I missing
something ? After all, it could be a pointer to the nth element
of a string, or the caller could on purpose allocate IDRs for
(ptr), (ptr + 1), and so on.

Thanks,
Guenter

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