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    SubjectRe: Oops in ext3_block_to_path.isra.40+0x26/0x11b
    On Fri, 16 Mar 2012, Jan Kara wrote:

    > > CPU is a Core i3 530, on a Gigabyte motherbord, 4 GB RAM. No ECC,
    > > unfortunately, so I can't rule out hardware bit rot. Distribution is
    > > a fairly stock Debian/unstable.
    > Hmm, is any mounting & unmounting happening during your backup? Because
    > the oops happened because sb->s_fs_info was NULL. Dissassembly shows:
    > 16: 48 8b 47 18 mov 0x18(%rdi),%rax
    > store sb->s_blocksize into RAX
    > 1a: 48 8b 8f b0 02 00 00 mov 0x2b0(%rdi),%rcx
    > store sb->s_fs_info into RCX
    > 21: 48 c1 e8 02 shr $0x2,%rax
    > This is division from EXT3_ADDR_PER_BLOCK() - RAX carries 1024 after
    > division so that looks correct.
    >
    > 25: 48 85 db test %rbx,%rbx
    > Now check passed i_block argument.
    >
    > 28: 41 89 c4 mov %eax,%r12d
    > 2b:* 8b b1 94 00 00 00 mov 0x94(%rcx),%esi <-- trapping ins
    > Try to get RCX->s_addr_per_block_bits...
    >
    > sb->s_fs_info is set when a superblock is mounted and cleared when
    > superblock gets unmounted and otherwise it is never changed. So most likely
    > it was some memory corruption clearing that pointer (I wouldn't really
    > suspect HW here).
    >
    > It somewhat looks like the issue described here:
    > http://lkml.indiana.edu/hypermail/linux/kernel/1202.3/00132.html
    >
    > Although there we had f_path.dentry (completely different structure) being
    > NULL. But similarity here is that something stomped NULL over our existing
    > structure.
    >
    > Linus, Jiri, that bug didn't get resolved, did it?

    I am not aware of anything, but I have a question -- George, did the
    machine get suspended/resumed before this happened?

    --
    Jiri Kosina
    SUSE Labs


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