6.9-stable review patch. If anyone has any objections, please let me know.
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From: Waiman Long longman@redhat.com
[ Upstream commit 82f0b6f041fad768c28b4ad05a683065412c226e ]
Commit 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing memory_section->usage") changed pfn_section_valid() to add a READ_ONCE() call around "ms->usage" to fix a race with section_deactivate() where ms->usage can be cleared. The READ_ONCE() call, by itself, is not enough to prevent NULL pointer dereference. We need to check its value before dereferencing it.
Link: https://lkml.kernel.org/r/20240626001639.1350646-1-longman@redhat.com Fixes: 5ec8e8ea8b77 ("mm/sparsemem: fix race in accessing memory_section->usage") Signed-off-by: Waiman Long longman@redhat.com Cc: Charan Teja Kalla quic_charante@quicinc.com Signed-off-by: Andrew Morton akpm@linux-foundation.org Signed-off-by: Sasha Levin sashal@kernel.org --- include/linux/mmzone.h | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-)
diff --git a/include/linux/mmzone.h b/include/linux/mmzone.h index a4f6f1fecc6f3..f8d89a021abc9 100644 --- a/include/linux/mmzone.h +++ b/include/linux/mmzone.h @@ -1976,8 +1976,9 @@ static inline int subsection_map_index(unsigned long pfn) static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) { int idx = subsection_map_index(pfn); + struct mem_section_usage *usage = READ_ONCE(ms->usage);
- return test_bit(idx, READ_ONCE(ms->usage)->subsection_map); + return usage ? test_bit(idx, usage->subsection_map) : 0; } #else static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn)