linux-kernel - [PATCH] m68k: fix "bad page state" oops on ColdFire boot

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Date:   Mon, 18 Jun 2018 16:04:26 +1000
From:   Greg Ungerer <gerg@...ux-m68k.org>
To:     mawilcox@...rosoft.com, linux-m68k@...r.kernel.org,
        linux-kernel@...r.kernel.org
Cc:     Greg Ungerer <gerg@...ux-m68k.org>
Subject: [PATCH] m68k: fix "bad page state" oops on ColdFire boot

Booting a ColdFire m68k core with MMU enabled causes a "bad page state"
oops since commit 1d40a5ea01d5 ("mm: mark pages in use for page tables"):

 BUG: Bad page state in process sh  pfn:01ce2
 page:004fefc8 count:0 mapcount:-1024 mapping:00000000 index:0x0
 flags: 0x0()
 raw: 00000000 00000000 00000000 fffffbff 00000000 00000100 00000200 00000000
 raw: 039c4000
 page dumped because: nonzero mapcount
 Modules linked in:
 CPU: 0 PID: 22 Comm: sh Not tainted 4.17.0-07461-g1d40a5ea01d5 #13

Fix by calling pgtable_page_dtor() in our __pte_free_tlb() code path,
so that the PG_table flag is cleared before we free the pte page.

Signed-off-by: Greg Ungerer <gerg@...ux-m68k.org>
CC: Matthew Wilcox <mawilcox@...rosoft.com>
---
 arch/m68k/include/asm/mcf_pgalloc.h | 1 +
 1 file changed, 1 insertion(+)

Matthew: I came across this thread at https://lkml.org/lkml/2018/6/17/163
         about a similar problem with openrisc. Based on that I came up
         with this fix for m68k/ColdFire. Fixes the issue for me.

diff --git a/arch/m68k/include/asm/mcf_pgalloc.h b/arch/m68k/include/asm/mcf_pgalloc.h
index 8b707c249026..8c441eb57b80 100644
--- a/arch/m68k/include/asm/mcf_pgalloc.h
+++ b/arch/m68k/include/asm/mcf_pgalloc.h
@@ -44,6 +44,7 @@ extern inline pmd_t *pmd_alloc_kernel(pgd_t *pgd, unsigned long address)
 static inline void __pte_free_tlb(struct mmu_gather *tlb, pgtable_t page,
 				  unsigned long address)
 {
+	pgtable_page_dtor(page);
 	__free_page(page);
 }
 
-- 
2.17.1