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

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Date:   Fri, 22 Jun 2018 15:33:35 -0700
From:   Guenter Roeck <linux@...ck-us.net>
To:     Matthew Wilcox <willy@...radead.org>
Cc:     Josef Bacik <jbacik@...com>,
        Geert Uytterhoeven <geert@...ux-m68k.org>,
        linux-m68k@...ts.linux-m68k.org, linux-kernel@...r.kernel.org
Subject: Re: 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