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Date: Tue, 23 Feb 2016 22:33:45 +0300
From: "Kirill A. Shutemov" <kirill@shutemov.name>
To: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Cc: 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,
        Sebastian Ott <sebott@linux.vnet.ibm.com>
Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also
 on PowerPC and ARM)
Message-ID: <20160223193345.GC21820@node.shutemov.name>
References: <20160211192223.4b517057@thinkpad>
 <20160211190942.GA10244@node.shutemov.name>
 <20160211205702.24f0d17a@thinkpad>
 <20160212154116.GA15142@node.shutemov.name>
 <56BE00E7.1010303@de.ibm.com>
 <20160212181640.4eabb85f@thinkpad>
 <20160223103221.GA1418@node.shutemov.name>
 <20160223191907.25719a4d@thinkpad>
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On Tue, Feb 23, 2016 at 07:19:07PM +0100, Gerald Schaefer wrote:
> I'll check with Martin, maybe it is actually trivial, then we can
> do a quick test it to rule that one out.

Oh. I found a bug in __split_huge_pmd_locked(). Although, not sure if it's
_the_ bug.

pmdp_invalidate() is called for the wrong address :-/
I guess that can be destructive on the architecture, right?

Could you check this?

diff --git a/mm/huge_memory.c b/mm/huge_memory.c
index 1c317b85ea7d..4246bc70e55a 100644
--- a/mm/huge_memory.c
+++ b/mm/huge_memory.c
@@ -2865,7 +2865,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 	pgtable = pgtable_trans_huge_withdraw(mm, pmd);
 	pmd_populate(mm, &_pmd, pgtable);
 
-	for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+	for (i = 0; i < HPAGE_PMD_NR; i++) {
 		pte_t entry, *pte;
 		/*
 		 * Note that NUMA hinting access restrictions are not
@@ -2886,9 +2886,9 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 		}
 		if (dirty)
 			SetPageDirty(page + i);
-		pte = pte_offset_map(&_pmd, haddr);
+		pte = pte_offset_map(&_pmd, haddr + i * PAGE_SIZE);
 		BUG_ON(!pte_none(*pte));
-		set_pte_at(mm, haddr, pte, entry);
+		set_pte_at(mm, haddr + i * PAGE_SIZE, pte, entry);
 		atomic_inc(&page[i]._mapcount);
 		pte_unmap(pte);
 	}
@@ -2938,7 +2938,7 @@ static void __split_huge_pmd_locked(struct vm_area_struct *vma, pmd_t *pmd,
 	pmd_populate(mm, pmd, pgtable);
 
 	if (freeze) {
-		for (i = 0; i < HPAGE_PMD_NR; i++, haddr += PAGE_SIZE) {
+		for (i = 0; i < HPAGE_PMD_NR; i++) {
 			page_remove_rmap(page + i, false);
 			put_page(page + i);
 		}
-- 
 Kirill A. Shutemov