linux-kernel - Re: [REGRESSION] nfsd crashing with 3.6.0-rc7 on PowerPC

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Date:	Tue, 2 Oct 2012 23:47:39 +0200
From:	Alexander Graf <agraf@...e.de>
To:	Nishanth Aravamudan <nacc@...ux.vnet.ibm.com>
Cc:	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-nfs@...r.kernel.org, Jan Kara <jack@...e.cz>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	LKML List <linux-kernel@...r.kernel.org>,
	"J. Bruce Fields" <bfields@...ldses.org>, anton@...ba.org,
	skinsbursky@...allels.com, bfields@...hat.com,
	linuxppc-dev <linuxppc-dev@...ts.ozlabs.org>
Subject: Re: [REGRESSION] nfsd crashing with 3.6.0-rc7 on PowerPC


On 02.10.2012, at 23:43, Nishanth Aravamudan wrote:

> Hi Ben,
> 
> On 02.10.2012 [10:58:29 +1000], Benjamin Herrenschmidt wrote:
>> On Mon, 2012-10-01 at 16:03 +0200, Alexander Graf wrote:
>>> Phew. Here we go :). It looks to be more of a PPC specific problem
>>> than it appeared as at first:
>> 
>> Ok, so I suspect the problem is the pushing down of the locks which
>> breaks with iommu backends that have a separate flush callback. In
>> that case, the flush moves out of the allocator lock.
>> 
>> Now we do call flush before we return, still, but it becomes racy
>> I suspect, but somebody needs to give it a closer look. I'm hoping
>> Anton or Nish will later today.
> 
> Started looking into this. If your suspicion were accurate, wouldn't the
> bisection have stopped at 0e4bc95d87394364f408627067238453830bdbf3
> ("powerpc/iommu: Reduce spinlock coverage in iommu_alloc and
> iommu_free")?
> 
> Alex, the error is reproducible, right?

Yes. I'm having a hard time to figure out if the reason my U4 based G5 Mac crashes and fails reading data is the same since I don't have a serial connection there, but I assume so.

> Does it go away by reverting
> that commit against mainline? Just trying to narrow down my focus.

The patch doesn't revert that easily. Mind to provide a revert patch so I can try?


Alex

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