linux-kernel - Re: md-raid 6.11.8 page fault oops

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Message-ID: <ef8bd4f9308dbf941076b2f7bd8a81590a09aa5e.camel@sapience.com>
Date: Tue, 19 Nov 2024 08:31:02 -0500
From: Genes Lists <lists@...ience.com>
To: Ojaswin Mujoo <ojaswin@...ux.ibm.com>
Cc: song@...nel.org, yukuai3@...wei.com, linux-raid@...r.kernel.org, 
	linux-kernel@...r.kernel.org, tytso@....edu, adilger.kernel@...ger.ca, 
	linux@...mhuis.info
Subject: Re: md-raid  6.11.8 page fault oops

On Tue, 2024-11-19 at 17:04 +0530, Ojaswin Mujoo wrote:
> > 
...

> >  (gdb) list *(rb_first+0x13)
> >   0xffffffff81de1af3 is in rb_first (lib/rbtree.c:473).
> >   468       struct rb_node  *n;
> >   469
> >   470       n = root->rb_node;
> >   471       if (!n)
> >   472           return NULL;
> >   473       while (n->rb_left)
> 
> Now this looks strange, we already make sure n is not NULL and then
> somehow this line ends up in
> 
>  BUG: unable to handle page fault for address: 0000000000200010
> 
> Now, decoding the code with an x86 vmlinux, I see the fauling opcode
> faulting:
> 
> Code starting with the faulting instruction
> ===========================================
>    0:   0f 1f 80 00 00 00 00    nopl   0x0(%rax)
>    7:   90                      nop
>    8:   90                      nop
>    9:   90                      nop
>    a:   90                      nop
>    b:   90                      nop
>    c:   90                      nop
>    d:   90                      nop
>    e:   90                      nop
>    f:   90                      nop
> 
> Now RAX is 0x200000 but I don't think the nopl instruction should
> have resulted
> in a mem access AFA my limited understanding of x86 ISA goes.
> 
> I also don't see nopl in my vmlinux in rb_first, my binary being
> compiled with
> gcc 8.5. Are you by chance using clang or higher version or higher
> optimization in gcc.
> 
> Regards,
> ojaswin

I am using Arch toolchain with 

   gcc 14.2.1+r134+gab884fffe3fc-1

I do not set CFLAGS_KERNEL  so compile options are the default.

thanks

gene



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