[REGRESSION] nfsd crashing with 3.6.0-rc7 on PowerPC

Alexander Graf agraf at suse.de
Tue Oct 2 00:03:06 EST 2012

On 28.09.2012, at 17:10, J. Bruce Fields wrote:

> On Fri, Sep 28, 2012 at 04:19:55AM +0200, Alexander Graf wrote:
>> On 28.09.2012, at 04:04, Linus Torvalds wrote:
>>> On Thu, Sep 27, 2012 at 6:55 PM, Alexander Graf <agraf at suse.de> wrote:
>>>> Below are OOPS excerpts from different rc's I tried. All of them crashed - all the way up to current Linus' master branch. I haven't cross-checked, but I don't remember any such behavior from pre-3.6 releases.
>>> Since you seem to be able to reproduce it easily (and apparently
>>> reliably), any chance you could just bisect it?
>>> Since I assume v3.5 is fine, and apparently -rc1 is already busted, a simple
>>>  git bisect start
>>>  git bisect good v3.5
>>>  git bisect bad v3.6-rc1
>>> will get you started on your adventure..
>> Heh, will give it a try :). The thing really does look quite bisectable.
>> It might take a few hours though - the machine isn't exactly fast by today's standards and it's getting late here. But I'll keep you updated.
> I doubt it's anything special about that workload, but just for kicks I
> tried a "git clone -ls" (cloning my linux tree to another directory on
> the same nfs filesystem), with server on 3.6.0-rc7, and didn't see
> anything interesting (just an xfs lockdep warning that looks like this
> one jlayton already reported:
> http://oss.sgi.com/archives/xfs/2012-09/msg00088.html
> )
> Any (even partial) bisection results would certainly be useful, thanks.

Phew. Here we go :). It looks to be more of a PPC specific problem than it appeared as at first:

b4c3a8729ae57b4f84d661e16a192f828eca1d03 is first bad commit
commit b4c3a8729ae57b4f84d661e16a192f828eca1d03
Author: Anton Blanchard <anton at samba.org>
Date:   Thu Jun 7 18:14:48 2012 +0000

    powerpc/iommu: Implement IOMMU pools to improve multiqueue adapter performance
    At the moment all queues in a multiqueue adapter will serialise
    against the IOMMU table lock. This is proving to be a big issue,
    especially with 10Gbit ethernet.
    This patch creates 4 pools and tries to spread the load across
    them. If the table is under 1GB in size we revert back to the
    original behaviour of 1 pool and 1 largealloc pool.
    We create a hash to map CPUs to pools. Since we prefer interrupts to
    be affinitised to primary CPUs, without some form of hashing we are
    very likely to end up using the same pool. As an example, POWER7
    has 4 way SMT and with 4 pools all primary threads will map to the
    same pool.
    The largealloc pool is reduced from 1/2 to 1/4 of the space to
    partially offset the overhead of breaking the table up into pools.
    Some performance numbers were obtained with a Chelsio T3 adapter on
    two POWER7 boxes, running a 100 session TCP round robin test.
    Performance improved 69% with this patch applied.
    Signed-off-by: Anton Blanchard <anton at samba.org>
    Signed-off-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>

:040000 040000 039ae3cbdcfded9c6b13e58a3fc67609f1b587b0 6755a8c4a690cc80dcf834d1127f21db925476d6 M	arch


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