Re: [BISECT] Kernel panic, RIP bitmap_create

[NeilBrown <neilb@suse.de>]

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On Wed, 2 May 2012 22:05:44 -0700 Karl Newman <siliconfiend@gmail.com> wrote:

> Hi,
> 
> I'm attempting to use kernel 3.4-rc? but keep running into a kernel panic on
> boot, with RIP pointing to bitmap_create. I tried 3.4-rc1, 3.4-rc4 and
> 3.4-rc5 and they all have the kernel panic, while 3.3.4 boots fine. I have
> my root on raid 5 with an internal bitmap, and the kernel panic occurs if I
> use the built-in kernel autodetect or during the root array assembly via
> mdadm inside a dracut-generated initramfs. I bisected it down to the
> following commit:
> 61a0d80ce4ab5b4fb9ecb38f1fb19654778b71ed
> 
> md/bitmap: discard CHUNK_BLOCK_SHIFT macro
> 
> Be redefining ->chunkshift as the shift from sectors to chunks rather than
> bytes to chunks, we can just use "bitmap->chunkshift" which is shorter than
> the macro call, and less indirect.
> 
> Signed-off-by: NeilBrown <neilb@suse.de>
> 
> My bisect testing including a scary commit where 2 of 3 drives had their
> UUIDs zeroed when I booted with it! Fortunately I found the mailing list
> archives with the solution and I was able to recover everything and keep
> bisecting (although I was tempted to quit and just give the range of
> commits...).
> 
> I hope this fix can make it into the next 3.4-rc kernel.

I do too, but first I would need to know what the fix is, and I cannot see
anything in that commit what would change the behaviour of md at all.

Do you have a copy of the full stack trace provided when Linux crashed?  That
could be useful.
Also what bitmap chunk size are you using? Maybe the output of
  mdadm -X
and
  mdadm -E

of one of the devices in the array would help.

Thanks a lot for the report and going to the trouble of bisecting, it is
really appreciated.

NeilBrown

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