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/mm-sparsemem-fix-race-in-accessing-memory_section-usage-v2.patch This patch will later appear in the mm-hotfixes-unstable branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm Before you just go and hit "reply", please: a) Consider who else should be cc'ed b) Prefer to cc a suitable mailing list as well c) Ideally: find the original patch on the mailing list and do a reply-to-all to that, adding suitable additional cc's *** Remember to use Documentation/process/submit-checklist.rst when testing your code *** The -mm tree is included into linux-next via the mm-everything branch at git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm and is updated there every 2-3 working days ------------------------------------------------------ From: Charan Teja Kalla <quic_charante@xxxxxxxxxxx> 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@xxxxxxxxxxx Fixes: f46edbd1b151 ("mm/sparsemem: add helpers track active portions of a section at boot") Signed-off-by: Charan Teja Kalla <quic_charante@xxxxxxxxxxx> Cc: Aneesh Kumar K.V <aneesh.kumar@xxxxxxxxxxxxx> Cc: Dan Williams <dan.j.williams@xxxxxxxxx> Cc: David Hildenbrand <david@xxxxxxxxxx> Cc: Mel Gorman <mgorman@xxxxxxxxxxxxxxxxxxx> Cc: Oscar Salvador <osalvador@xxxxxxx> Cc: Vlastimil Babka <vbabka@xxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> --- 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@xxxxxxxxxxx are mm-sparsemem-fix-race-in-accessing-memory_section-usage.patch mm-sparsemem-fix-race-in-accessing-memory_section-usage-v2.patch