The patch titled Subject: mm/sparsemem: fix race in accessing memory_section->usage has been added to the -mm mm-hotfixes-unstable branch. Its filename is mm-sparsemem-fix-race-in-accessing-memory_section-usage-v2.patch

This patch will shortly appear at https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches...

This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------ From: Charan Teja Kalla quic_charante@quicinc.com Subject: mm/sparsemem: fix race in accessing memory_section->usage Date: Fri, 27 Oct 2023 16:19:38 +0530

use kfree_rcu() in place of synchronize_rcu(), per David

Link: https://lkml.kernel.org/r/1698403778-20938-1-git-send-email-quic_charante@qu... Fixes: f46edbd1b151 ("mm/sparsemem: add helpers track active portions of a section at boot") Signed-off-by: Charan Teja Kalla quic_charante@quicinc.com Cc: Aneesh Kumar K.V aneesh.kumar@linux.ibm.com Cc: Dan Williams dan.j.williams@intel.com Cc: David Hildenbrand david@redhat.com Cc: Mel Gorman mgorman@techsingularity.net Cc: Oscar Salvador osalvador@suse.de Cc: Vlastimil Babka vbabka@suse.cz Cc: stable@vger.kernel.org Signed-off-by: Andrew Morton akpm@linux-foundation.org ---

include/linux/mmzone.h | 3 ++- mm/sparse.c | 5 ++--- 2 files changed, 4 insertions(+), 4 deletions(-)

--- a/include/linux/mmzone.h~mm-sparsemem-fix-race-in-accessing-memory_section-usage-v2 +++ a/include/linux/mmzone.h @@ -1770,6 +1770,7 @@ static inline unsigned long section_nr_t #define SUBSECTION_ALIGN_DOWN(pfn) ((pfn) & PAGE_SUBSECTION_MASK)

struct mem_section_usage { + struct rcu_head rcu; #ifdef CONFIG_SPARSEMEM_VMEMMAP DECLARE_BITMAP(subsection_map, SUBSECTIONS_PER_SECTION); #endif @@ -1963,7 +1964,7 @@ static inline int pfn_section_valid(stru { int idx = subsection_map_index(pfn);

- return test_bit(idx, ms->usage->subsection_map); + return test_bit(idx, READ_ONCE(ms->usage)->subsection_map); } #else static inline int pfn_section_valid(struct mem_section *ms, unsigned long pfn) --- a/mm/sparse.c~mm-sparsemem-fix-race-in-accessing-memory_section-usage-v2 +++ a/mm/sparse.c @@ -806,9 +806,8 @@ static void section_deactivate(unsigned * was allocated during boot. */ if (!PageReserved(virt_to_page(ms->usage))) { - synchronize_rcu(); - kfree(ms->usage); - ms->usage = NULL; + kfree_rcu(ms->usage, rcu); + WRITE_ONCE(ms->usage, NULL); } memmap = sparse_decode_mem_map(ms->section_mem_map, section_nr); } _

Patches currently in -mm which might be from quic_charante@quicinc.com are

mm-sparsemem-fix-race-in-accessing-memory_section-usage.patch mm-sparsemem-fix-race-in-accessing-memory_section-usage-v2.patch