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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: 1180e732c985ed3c8866d2fd9e02b619848404a0
Gitweb: https://git.kernel.org/tip/1180e732c985ed3c8866d2fd9e02b619848404a0
Author: Peter Zijlstra <peterz@infradead.org>
AuthorDate: Thu, 26 Nov 2020 17:21:30 +01:00
Committer: Dave Hansen <dave.hansen@linux.intel.com>
CommitterDate: Thu, 15 Dec 2022 10:37:27 -08:00

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@infradead.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))
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