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    Subject[OOPS] Re: Linux 2.4.5-ac1
    On Sat, May 26, 2001 at 10:58:25PM +0100, you [Alan Cox] claimed:
    > o Free the initial ramdisk correctly

    Who made this fix, or who can I contact?

    I have a reproducible oops on 2.4.4ac17 (see for
    details) that seems to be related:

    (1)Unable to handle kernel NULL pointer
    dereference at virtual address 00000013

    >>EIP; c02997f6 <__devices_1045+5a/a8> <=====
    Trace; c0136447 <ioctl_by_bdev+77/90>
    Trace; c017fec3 <batch_entropy_process+b3/c0>
    Trace; c0118769 <__run_task_queue+49/60>
    Trace; c011b0f6 <update_wall_time+16/50>
    Trace; c011b304 <timer_bh+24/250>
    Trace; c011868c <bh_action+1c/60>
    Trace; c0118596 <tasklet_hi_action+36/60>
    Trace; c011849b <do_softirq+5b/80>
    Trace; c010832f <do_IRQ+9f/b0>
    Trace; c0106f14 <ret_from_intr+0/20>
    Trace; c0199756 <rd_make_request+d6/100>
    Trace; c01330d6 <try_to_free_buffers+f6/140>
    Trace; c0131447 <getblk+e7/100>
    Trace; c0122cf5 <truncate_list_pages+145/170>
    Trace; c01416db <destroy_inode+1b/20>
    Trace; c0142b81 <iput+121/130>
    Trace; c0136641 <blkdev_put+71/a0>
    Trace; c013484a <kill_super+da/100>
    Trace; c0134ab0 <do_umount+e0/f0>
    Trace; c0105000 <do_linuxrc+0/e0>
    Trace; c01177e6 <sys_waitpid+16/20>
    Trace; c0105000 <do_linuxrc+0/e0>
    Trace; c01051da <prepare_namespace+fa/120>
    Trace; c010520e <init+e/140>
    Trace; c0105000 <do_linuxrc+0/e0>
    Trace; c01056a6 <kernel_thread+26/30>
    Trace; c0105200 <init+0/140>
    Code; c02997f6 <__devices_1045+5a/a8>
    00000000 <_EIP>:
    Code; c02997f6 <__devices_1045+5a/a8> <=====
    0: 8b 40 10 mov 0x10(%eax),%eax <=====
    Code; c02997f9 <__devices_1045+5d/a8>
    3: 83 f8 02 cmp $0x2,%eax
    Code; c02997fc <__devices_1045+60/a8>
    6: 7e 62 jle 6a <_EIP+0x6a> c0299860
    Code; c02997fe <__devices_1045+62/a8>
    8: b8 f0 ff ff ff mov $0xfffffff0,%eax
    Code; c0299803 <__devices_1045+67/a8>
    d: eb 74 jmp 83 <_EIP+0x83> c0299879
    Code; c0299805 <__devices_1045+69/a8>
    f: 85 c9 test %ecx,%ecx
    Code; c0299807 <__devices_1045+6b/a8>
    11: b8 ea ff 00 00 mov $0xffea,%eax

    Judging from the stack trace, I suspect that after kill_super is called (and
    hence, root device invalidated and freed), a function that that assumes a
    valid rootdev (ioctl_by_bdev) is called. Rdev is NULL, and hence the null
    ptr deref. Is this anywhere near the truth?

    -- v --

    PS: A this is a 600Mhz Xeon w/ 256MB RAM. Right after boot I did
    'diff -nauR linux-2.4.5 linux-2.4.4ac17' on redhat 2.4.2-2, and it never

    root@machine:/poista>diff -nauR linux-2.4.5 linux-2.4.4ac17
    zsh: terminated diff -nauR linux-2.4.5 linux-2.4.4ac17
    total used free shared buffers cached
    Mem: 255572 253140 2432 0 8332 215108
    -/+ buffers/cache: 29700 225872
    Swap: 0 0 0
    root@machine:/poista>uname -a
    Linux machine 2.4.2-2 #1 Sun Apr 8 20:41:30 EDT 2001 i686 unknown
    root@machine:/poista>dmesg | tail -2
    Out of Memory: Killed process 804 (xfs).
    Out of Memory: Killed process 15857 (diff).

    So diff (which used very little RAM) filled the _cache_ and OOM rambo kicked
    in. Pretty embarrassing to say at least...
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