[PATCH v2 07/23 replacement] mips: add pte_unmap() to balance pte_offset_map()

From: Hugh Dickins <hughd@google•com>
To: Andrew Morton <akpm@linux-foundation•org>
Cc: Nathan Chancellor <nathan@kernel•org>,
	Hugh Dickins <hughd@google•com>,
	 Mike Kravetz <mike.kravetz@oracle•com>,
	Mike Rapoport <rppt@kernel•org>,
	 "Kirill A. Shutemov" <kirill.shutemov@linux•intel.com>,
	 Matthew Wilcox <willy@infradead•org>,
	David Hildenbrand <david@redhat•com>,
	 Suren Baghdasaryan <surenb@google•com>,
	 Qi Zheng <zhengqi.arch@bytedance•com>,
	 Peter Zijlstra <peterz@infradead•org>,
	 Russell King <linux@armlinux•org.uk>,
	 Catalin Marinas <catalin.marinas@arm•com>,
	Will Deacon <will@kernel•org>,
	 Geert Uytterhoeven <geert@linux-m68k•org>,
	 Greg Ungerer <gerg@linux-m68k•org>,
	Michal Simek <monstr@monstr•eu>,
	 Thomas Bogendoerfer <tsbogend@alpha•franken.de>,
	 Helge Deller <deller@gmx•de>,
	John David Anglin <dave.anglin@bell•net>,
	 "Aneesh Kumar K.V" <aneesh.kumar@linux•ibm.com>,
	 Michael Ellerman <mpe@ellerman•id.au>,
	 Alexandre Ghiti <alexghiti@rivosinc•com>,
	 Palmer Dabbelt <palmer@dabbelt•com>,
	Heiko Carstens <hca@linux•ibm.com>,
	 Christian Borntraeger <borntraeger@linux•ibm.com>,
	 Claudio Imbrenda <imbrenda@linux•ibm.com>,
	 Alexander Gordeev <agordeev@linux•ibm.com>,
	 John Paul Adrian Glaubitz <glaubitz@physik•fu-berlin.de>,
	 "David S. Miller" <davem@davemloft•net>,
	Chris Zankel <chris@zankel•net>,
	 Max Filippov <jcmvbkbc@gmail•com>, Yu Zhao <yuzhao@google•com>,
	 x86@kernel•org, linux-arm-kernel@lists•infradead.org,
	 linux-ia64@vger•kernel.org, linux-m68k@lists•linux-m68k.org,
	 linux-mips@vger•kernel.org, linux-parisc@vger•kernel.org,
	 linuxppc-dev@lists•ozlabs.org, linux-riscv@lists•infradead.org,
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	 sparclinux@vger•kernel.org, linux-kernel@vger•kernel.org,
	 linux-mm@kvack•org
Subject: [PATCH v2 07/23 replacement] mips: add pte_unmap() to balance pte_offset_map()
Date: Thu, 15 Jun 2023 16:02:43 -0700 (PDT)	[thread overview]
Message-ID: <addfcb3-b5f4-976e-e050-a2508e589cfe@google.com> (raw)
In-Reply-To: <76b41825-30fa-b9e8-d043-2affcba24317@google.com>

To keep balance in future, __update_tlb() remember to pte_unmap() after
pte_offset_map().  This is an odd case, since the caller has already done
pte_offset_map_lock(), then mips forgets the address and recalculates it;
but my two naive attempts to clean that up did more harm than good.

Tested-by: Nathan Chancellor <nathan@kernel•org>
Signed-off-by: Hugh Dickins <hughd@google•com>
---
Andrew, please replace my mips patch, and its build warning fix patch,
in mm-unstable by this less ambitious but working replacement - thanks.

 arch/mips/mm/tlb-r4k.c | 12 ++++++++++--
 1 file changed, 10 insertions(+), 2 deletions(-)

diff --git a/arch/mips/mm/tlb-r4k.c b/arch/mips/mm/tlb-r4k.c
index 1b939abbe4ca..93c2d695588a 100644
--- a/arch/mips/mm/tlb-r4k.c
+++ b/arch/mips/mm/tlb-r4k.c
@@ -297,7 +297,7 @@ void __update_tlb(struct vm_area_struct * vma, unsigned long address, pte_t pte)
 	p4d_t *p4dp;
 	pud_t *pudp;
 	pmd_t *pmdp;
-	pte_t *ptep;
+	pte_t *ptep, *ptemap = NULL;
 	int idx, pid;
 
 	/*
@@ -344,7 +344,12 @@ void __update_tlb(struct vm_area_struct * vma, unsigned long address, pte_t pte)
 	} else
 #endif
 	{
-		ptep = pte_offset_map(pmdp, address);
+		ptemap = ptep = pte_offset_map(pmdp, address);
+		/*
+		 * update_mmu_cache() is called between pte_offset_map_lock()
+		 * and pte_unmap_unlock(), so we can assume that ptep is not
+		 * NULL here: and what should be done below if it were NULL?
+		 */
 
 #if defined(CONFIG_PHYS_ADDR_T_64BIT) && defined(CONFIG_CPU_MIPS32)
 #ifdef CONFIG_XPA
@@ -373,6 +378,9 @@ void __update_tlb(struct vm_area_struct * vma, unsigned long address, pte_t pte)
 	tlbw_use_hazard();
 	htw_start();
 	flush_micro_tlb_vm(vma);
+
+	if (ptemap)
+		pte_unmap(ptemap);
 	local_irq_restore(flags);
 }
 
-- 
2.35.3


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