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Date: Wed, 17 Feb 2016 17:04:56 +0200
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: Sebastian Ott <sebott@linux.vnet.ibm.com>,
        Andrea Arcangeli <aarcange@redhat.com>,
        Christian Borntraeger <borntraeger@de.ibm.com>,
        "Kirill A. Shutemov" <kirill.shutemov@linux.intel.com>,
        linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        "Aneesh Kumar K.V" <aneesh.kumar@linux.vnet.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Michael Ellerman <mpe@ellerman.id.au>,
        Benjamin Herrenschmidt <benh@kernel.crashing.org>,
        Paul Mackerras <paulus@samba.org>, linuxppc-dev@lists.ozlabs.org,
        Catalin Marinas <catalin.marinas@arm.com>,
        Will Deacon <will.deacon@arm.com>,
        linux-arm-kernel@lists.infradead.org,
        Martin Schwidefsky <schwidefsky@de.ibm.com>,
        Heiko Carstens <heiko.carstens@de.ibm.com>, linux-s390@vger.kernel.org
Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also
 on PowerPC and ARM)
Message-ID: <20160217150456.GA15882@node.shutemov.name>
References: <20160211205702.24f0d17a@thinkpad>
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 <56BE00E7.1010303@de.ibm.com>
 <20160212181640.4eabb85f@thinkpad>
 <20160212231510.GB15142@node.shutemov.name>
 <alpine.LFD.2.20.1602131238260.1910@schleppi>
 <20160215113159.GA28832@node.shutemov.name>
 <20160215193702.4a15ed5e@thinkpad>
 <20160215213526.GA9766@node.shutemov.name>
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On Tue, Feb 16, 2016 at 05:24:44PM +0100, Gerald Schaefer wrote:
> On Mon, 15 Feb 2016 23:35:26 +0200
> "Kirill A. Shutemov" <kirill@shutemov.name> wrote:
> 
> > Is there any chance that I'll be able to trigger the bug using QEMU?
> > Does anybody have an QEMU image I can use?
> > 
> 
> I have no image, but trying to reproduce this under virtualization may
> help to trigger this also on other architectures. After ruling out IPI
> vs. fast_gup I do not really see why this should be arch-specific, and
> it wouldn't be the first time that we hit subtle races first on s390, due
> to our virtualized environment (my test case is make -j20 with 10 CPUs and
> 4GB of memory, no swap).

Could you post your kernel config?

It would be nice also to check if disabling split_huge_page() would make
any difference:

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index a75081ca31cf..26d2b7b21021 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -3364,6 +3364,8 @@ int split_huge_page_to_list(struct page *page, struct list_head *list)
 	bool mlocked;
 	unsigned long flags;
 
+	return -EBUSY;
+
 	VM_BUG_ON_PAGE(is_huge_zero_page(page), page);
 	VM_BUG_ON_PAGE(!PageAnon(page), page);
 	VM_BUG_ON_PAGE(!PageLocked(page), page);
-- 
 Kirill A. Shutemov