linux-kernel - Re: [BUG] random kernel crashes after THP rework on s390 (maybe also on PowerPC and ARM)

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Message-ID: <20160223193345.GC21820@node.shutemov.name>
Date:	Tue, 23 Feb 2016 22:33:45 +0300
From:	"Kirill A. Shutemov" <kirill@...temov.name>
To:	Gerald Schaefer <gerald.schaefer@...ibm.com>
Cc:	Christian Borntraeger <borntraeger@...ibm.com>,
	"Kirill A. Shutemov" <kirill.shutemov@...ux.intel.com>,
	linux-mm@...ck.org, linux-kernel@...r.kernel.org,
	"Aneesh Kumar K.V" <aneesh.kumar@...ux.vnet.ibm.com>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Michael Ellerman <mpe@...erman.id.au>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Paul Mackerras <paulus@...ba.org>,
	linuxppc-dev@...ts.ozlabs.org,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	linux-arm-kernel@...ts.infradead.org,
	Martin Schwidefsky <schwidefsky@...ibm.com>,
	Heiko Carstens <heiko.carstens@...ibm.com>,
	linux-s390@...r.kernel.org,
	Sebastian Ott <sebott@...ux.vnet.ibm.com>
Subject: Re: [BUG] random kernel crashes after THP rework on s390 (maybe also
 on PowerPC and ARM)

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