linux-kernel - Re: Crash with kfree(null) on MacBook? kobject_set_name

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Message-ID: <BANLkTincyn_2FrSYwJnNNnYE9WdyVzoHFA@mail.gmail.com>
Date:	Mon, 11 Apr 2011 21:38:02 +0200
From:	Rafał Miłecki <zajec5@...il.com>
To:	Linus Torvalds <torvalds@...ux-foundation.org>
Cc:	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Andy Botting <andy@...ybotting.com>
Subject: Re: Crash with kfree(null) on MacBook? kobject_set_name_vargs

W dniu 11 kwietnia 2011 19:41 użytkownik Linus Torvalds
<torvalds@...ux-foundation.org> napisał:
> 2011/4/10 Rafał Miłecki <zajec5@...il.com>:
>> I'm writing new axi bus driver and one of the early testers reported
>> it crashing for him. Andy is using MacBook and backtrace+debugging
>> pretty clearly point to kfree being called on null string.
>>
>> The most interesting part of code is:
>> axi_info("[axi_register_cores][%d] current name: %s\n", i, core->dev.kobj.name);
>> axi_info("[axi_register_cores][%d] calling dev_set_name with %d, %d
>> for 0x%03X\n", i, 0/*bus->busnumber*/, dev_id, core->id.id);
>> err = dev_set_name(&core->dev, "axi%d:%d", 0/*bus->busnumber*/, dev_id);
>> axi_info("[axi_register_cores][%d] dev_set_name result: %d\n", i, err);
>>
>> The result is:
>> [axi_register_cores][1] current name: (null)
>> [axi_register_cores][1] calling dev_set_name with 0, 0 for 0x812
>> BUG: unable to handle kernel paging request at ffffeba400000000
>> IP: [<ffffffff8108c4d4>] kfree+0x2a/0x8a
>>
>> Whole code: http://pastie.org/1779473
>> Whole result: http://pastie.org/1779416
>>
>> Can you help me with this issue, please? On my machine everything goes fine:
>> [axi_register_cores][1] current name: (null)
>> [axi_register_cores][1] calling dev_set_name with 0, 0 for 0x812
>> [axi_register_cores][1] dev_set_name result: 0
>> [axi_register_cores][1] Register dev for core 0x812
>>
>> bcopeland on #linux-wireless suggested turning on SLAB or SLUB. Is
>> this going to provide some interesting info?
>
> The disassembly of the oopsing code (kfree()) is:
>
>   0:   41 54                   push   %r12
>   2:   48 83 ff 10             cmp    $0x10,%rdi
>   6:   55                      push   %rbp
>   7:   53                      push   %rbx
>   8:   48 89 fb                mov    %rdi,%rbx
>   b:   76 78                   jbe    0x85
>   d:   9c                      pushfq
>   e:   5d                      pop    %rbp
>   f:   fa                      cli
>  10:   e8 85 21 f9 ff          callq  0xfffffffffff9219a
>  15:   48 ba 00 00 00 00 00    movabs $0xffffea0000000000,%rdx
>  1c:   ea ff ff
>  1f:   48 c1 e8 0c             shr    $0xc,%rax
>  23:   48 6b c0 38             imul   $0x38,%rax,%rax
>  27:   48 01 d0                add    %rdx,%rax
>  2a:*  48 8b 10                mov    (%rax),%rdx     <-- trapping instruction
>  2d:   66 85 d2                test   %dx,%dx
>  30:   79 04                   jns    0x36
>
> and from that you can see that the parameter that was passed in to
> kfree (which was originally in %rdi) is now in %rbx.
>
> That, in turn, is 0x202.
>
> So it's not NULL. The fact that
>
>  axi_info("[axi_register_cores][%d] current name: %s\n", i,
> core->dev.kobj.name);
>
> prints out NULL is because the string printout code does this:
>
>        if ((unsigned long)s < PAGE_SIZE)
>                s = "(null)";
>
>
> which admittedly is not very helpful in this case (but it's usually
> nicer than just oopsing).
>
> So code->dev.kobj.name is corrupt even before.
>
> Where that corruption comes from, I have no idea, but there is no
> point in blaming kfree() or dev_set_name().

Thank you Linus, now when you made it clear to me that NULL ~!= NULL,
I realized I didn't zeroed struct which contains struct dev.

struct axi_device core;
vs.
struct axi_device core = { };

-- 
Rafał
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