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    SubjectNULL pointer dereference in ext4_ext_remove_space on 3.5.1
    Hi list,

    I was moving and deleting some files between two of my ext4 partitions
    when it suddenly crashed and dropped me into an kernel oops screen
    (below). I'm using ext4 on kernel 3.5.1 (Arch Linux). Both likely
    suspect file systems are stored on LVM2, mounted with
    data=writeback,errors=remount-ro,noatime

    EXT4-fs (sda3): mounted filesystem with writeback data mode. Opts: (null)
    EXT4-fs (dm-1): mounted filesystem with writeback data mode. Opts:
    errors=remount-ro
    EXT4-fs (dm-0): mounted filesystem with writeback data mode. Opts:
    errors=remount-ro

    I can't be bothered to transcribe all those 64-bit pointer values, but
    here's the human-readable parts (screen shot links below):

    BUG: unable to handle kernel NULL pointer dereference at 000...00028
    IP: [...] ext4_ext_remove_space+0xaa4/0xef0 [ext4]
    PGD ... PUD ... PMD 0
    Oops: 0000 [#1] PREEMPT SMP
    CPU 2
    Modules linked in: [... bazillion modules ...]

    Pid: 3687, comm: rm Tainted: G C 3.5.1-1-ARCH #1 System
    manufacturer System Product Name/M3A76-CM
    RIP: 0010:[...] [...] ext4_ext_remove_space
    [... CPU register dump ...]
    Process rm (pid: 3687, threadinfo ..., task ...)
    Call Trace:
    [...] ext4_ext_truncate+0x183/0x1c0 [ext]
    [...] ? ext4_mark_inode_dirty+0x7e/0x230 [ext4]
    [...] ext4_truncate+0x135/0x140 [ext4]
    [...] ext4_evict_inode+0x40f/0x4e0 [ext4]
    [...] evict+0xb8/0x1b0
    [...] iput+0x105/0x210
    [...] do_unlinkat+0x1b/0x50
    [...] ? flip_close+0x66/0xa0
    [...] sys_unlinkat+0x1b/0x50
    [...] system_call_fastpath+0x16/0x1b
    Code: [...]
    RIP [...] ext4_ext_remove_space+0xaa4/0xef0 [ext4]
    CR2: 000...00028

    Taint flag C is caused by the staging r8712u driver (Realtek USB Wi-Fi
    adapter). But I wasn't even using it today, so I doubt that had
    anything to do with it.

    Some "screen shots" taken with a webcam (warning: CSI "zoom & enhance"
    technology required)
    http://ompldr.org/vZjQ3dw
    http://ompldr.org/vZjQ3eg
    http://ompldr.org/vZjQ4MA
    http://ompldr.org/vZjQ3eQ
    http://ompldr.org/vZjQ3eA

    Regards,
    Marti


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