Re: Oops while modprobing phy fixed module

[Gabriel C <nix.or.die@googlemail.com>]

Satyam Sharma wrote:
> Hi Gabriel,
>
> On 7/16/07, Gabriel C <nix.or.die@googlemail.com> wrote:
>
>   
>> ( http://194.231.229.228/Oops.txt )
>>     
>
>   
>> I cannot reproduce this on plain 2.6.22 so I've started to bisect the
>> problem.
>>     
>
> Could you reproduce this oops at will at the "bad" points? [ Note that
> git-bisect isn't quite applicable to bugs that are not 100% reproducible.
> The ones that passed as "good" may have passed only because the
> bug didn't get triggered on that particular test. Also, a perfectly good
> commit could get unnecessarily marked "bad" because the bug
> happened to get triggered for it ... so it's not quite trust-worthy for
> your case. ]
>   

Yes all marked 'bad' ponts have the Oops , at least here.

>   
>> Here the bisect result:
>>
>> 3007e997de91ec59af39a3f9c91595b31ae6e08b is first bad commit
>> commit 3007e997de91ec59af39a3f9c91595b31ae6e08b
>> Author: Tejun Heo <htejun@gmail.com>
>> Date:   Thu Jun 14 04:27:23 2007 +0900
>>
>>     sysfs: use sysfs_mutex to protect the sysfs_dirent tree
>>
>>     As kobj sysfs dentries and inodes are gonna be made reclaimable,
>>     i_mutex can't be used to protect sysfs_dirent tree.  Use sysfs_mutex
>>     globally instead.  As the whole tree is protected with sysfs_mutex,
>>     there is no reason to keep sysfs_rename_sem.  Drop it.
>>
>>     While at it, add docbook comments to functions which require
>>     sysfs_mutex locking.
>>
>>     Signed-off-by: Tejun Heo <htejun@gmail.com>
>>     Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>
>>
>> :040000 040000 9deba7887752bc343cc4f5dea2dac70e895ea8b6
>> 75340b6e18c1ada500bb1a2b99ee88fd93ebae8c M      fs
>>     
>
> Hmm, I don't see why this one could introduce an oops in SLUB,
> but it's doing some locking-related stuff, and if it didn't get it right,
> the resulting races /could/ lead to some oops. But ... a recently
> posted patch (http://lkml.org/lkml/2007/7/16/204) from Akinobu
> Mita does point to an oops that was introduced by commit
> 0c096b507f15397da890051ee73de4266d3941fb that belongs to the
> same patchset -- kmem_cache_free(NULL) is illegal and so will oops.
> A curious coincidence is that you do see sysfs_new_dirent() in the
> stack trace there, but the oops there is in kmem_cache_free(), not
> kmem_cache_zalloc() as your dmesg output indicated.
>
> Try that patch anyway, but I don't think that'll solve your problem --
> if it was, you would've been seeing "unable to handle kernel NULL
> pointer dereference" but what you've been posting is "unable to
> handle kernel paging request at virtual address <non_null_ptr>" ...
>   

I will try this patch and look whatever it helps.

> Gaah.
>
> And the worst thing about it all is that we're not able to trigger the
> oops with debugging options -- that backtrace is horrible, so I'd
> suggest CONFIG_FRAME_POINTER, at the very least. And also
> perhaps DEBUG_INFO while we're at it -- that'll make later
> analysis easier, if nothing else.
>   

I will enable DEBUG option and reproduce in a bit.

> [ BTW I couldn't even get my compiler to generate the same
> "Code:" as we saw in your dmesg (I suspect all the oopsen
> have occurred with DEBUG=n, yes?) so my earlier analysis
> that suspected SLUB's page->lockless_freelist in slab_alloc()
> as the source of that invalid kernel address was actually
> based on some human-work rather than simple tools doing
> their thing. Gaah, again! ]
>   

My original report ( also first Oops posted here ) was with DEBUG_KERNEL=y
but as I said I will reproduce in a bit with all the DEBUG options you
suggested.

Shall I enable DEBUG_PAGEALLOC too ?

> I'm thoroughly mystified ... Christoph? Tejun? Someone?
>
> Satyam
>
>   

Gabriel