linux-kernel - [tip: x86/mm] mm/gup: Fix the lockless PMD access

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Date:   Wed, 02 Nov 2022 09:12:39 -0000
From:   "tip-bot2 for Peter Zijlstra" <tip-bot2@...utronix.de>
To:     linux-tip-commits@...r.kernel.org
Cc:     "Peter Zijlstra (Intel)" <peterz@...radead.org>, x86@...nel.org,
        linux-kernel@...r.kernel.org
Subject: [tip: x86/mm] mm/gup: Fix the lockless PMD access

The following commit has been merged into the x86/mm branch of tip:

Commit-ID:     4fff2c7e6b8e91e00838b145d08353dd8a1893c1
Gitweb:        https://git.kernel.org/tip/4fff2c7e6b8e91e00838b145d08353dd8a1893c1
Author:        Peter Zijlstra <peterz@...radead.org>
AuthorDate:    Thu, 26 Nov 2020 17:21:30 +01:00
Committer:     Peter Zijlstra <peterz@...radead.org>
CommitterDate: Tue, 01 Nov 2022 13:44:02 +01:00

mm/gup: Fix the lockless PMD access

On architectures where the PTE/PMD is larger than the native word size
(i386-PAE for example), READ_ONCE() can do the wrong thing. Use
pmdp_get_lockless() just like we use ptep_get_lockless().

Signed-off-by: Peter Zijlstra (Intel) <peterz@...radead.org>
Link: https://lkml.kernel.org/r/20221022114424.906110403%40infradead.org
---
 kernel/events/core.c | 2 +-
 mm/gup.c             | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/kernel/events/core.c b/kernel/events/core.c
index 4ec3717..b0d3842 100644
--- a/kernel/events/core.c
+++ b/kernel/events/core.c
@@ -7306,7 +7306,7 @@ static u64 perf_get_pgtable_size(struct mm_struct *mm, unsigned long addr)
 		return pud_leaf_size(pud);
 
 	pmdp = pmd_offset_lockless(pudp, pud, addr);
-	pmd = READ_ONCE(*pmdp);
+	pmd = pmdp_get_lockless(pmdp);
 	if (!pmd_present(pmd))
 		return 0;
 
diff --git a/mm/gup.c b/mm/gup.c
index fe195d4..ff8b223 100644
--- a/mm/gup.c
+++ b/mm/gup.c
@@ -2808,7 +2808,7 @@ static int gup_pmd_range(pud_t *pudp, pud_t pud, unsigned long addr, unsigned lo
 
 	pmdp = pmd_offset_lockless(pudp, pud, addr);
 	do {
-		pmd_t pmd = READ_ONCE(*pmdp);
+		pmd_t pmd = pmdp_get_lockless(pmdp);
 
 		next = pmd_addr_end(addr, end);
 		if (!pmd_present(pmd))