On Fri, Jun 18, 2010 at 1:19 PM, Manish Katiyar <mkati...@gmail.com> wrote:
> On Fri, Jun 18, 2010 at 10:11 AM, Prasad Joshi <prasadjoshi...@gmail.com>
> wrote:
> > Hi All,
> >
> > I am trying to understand a a kernel oops report. Here are some of the
> > fields from the report
> >
> > BUG: unable to handle kernel NULL pointer dereference at 0000000000000034
> > Oops: 0000 [#1] SMP
> > Pid: 6478, comm: cp Tainted: P 2.6.31.5-127.fc12.x86_64 #1 Inspiron 1525
> > RIP: 0010:[<ffffffff810faac1>] [<ffffffff810faac1>]
> do_sys_open+0x7a/0x10f
> > CR2: 0000000000000034
> >
> > As I know, when a page fault occurs, the address the program attempted to
> > access is stored in the CR2 register. So probably the pointer is pointing
> to
> > address 0034 and is being access.
> >
> > The BUG string is bit confusing, it says NULL pointer dereference at
> 0034, I
> > know the address 00034 is not valid but why is it interpreted as NULL
> > pointer? The NULL pointer as I know should point to address 0.
>
> As ppl have already mentioned, this is some offset into a structure.
> Next thing you can try is to do a disas do_sys_open and find out which
> member/structure is being accessed which has this offset. You can also
> try to get the assembly instructions from the "code" dumped. if you
> already have the source code for your running kernel you can also try
> "l *do_sys_open+0x7a".
>
>
Thanks Manish for your reply. The problem was with the return value in FS
create() call. The create() call was returning the +ve error code. I looked
into some of the other file systems, they use PTR_ERR to return the error
code. Basically the -ve error code is assigned to unsigned long causing,
thus converting it in a big number.
struct file *f = do_filp_open(dfd, tmp, flags, mode, 0);
if (IS_ERR(f)) {
put_unused_fd(fd);
fd = PTR_ERR(f);
} else {
fsnotify_open(f->f_path.dentry); <=== OOPs
fd_install(fd, f);
}
So IS_ERR() was returning false and causing panic in else path.
Thanks a lot for your help.
Regards,
Prasad
>
> >
> > Thanks and Regards,
> > Prasad
> >
>
>
>
> --
> Thanks -
> Manish
> ==================================
> [$\*.^ -- I miss being one of them
> ==================================
>
