riscv: mm: Take memory hotplug read-lock during kernel page table dump

During memory hot remove, the ptdump functionality can end up touching
stale data. Avoid any potential crashes (or worse), by holding the
memory hotplug read-lock while traversing the page table.

This change is analogous to arm64's commit bf2b59f60ee1 ("arm64/mm:
Hold memory hotplug lock while walking for kernel page table dump").

Reviewed-by: David Hildenbrand <david@redhat.com>
Reviewed-by: Oscar Salvador <osalvador@suse.de>
Signed-off-by: Björn Töpel <bjorn@rivosinc.com>
Link: https://lore.kernel.org/r/20240605114100.315918-8-bjorn@kernel.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>

diff --git a/arch/riscv/mm/ptdump.c b/arch/riscv/mm/ptdump.c
index 1289cc6d3700cde8d68f022612d3e4229dd768b6..9d5f657a251b328dffb0ea807b4576ab15cc4e92 100644 (file)
--- a/arch/riscv/mm/ptdump.c
+++ b/arch/riscv/mm/ptdump.c
@@ -6,6 +6,7 @@
 #include <linux/efi.h>
 #include <linux/init.h>
 #include <linux/debugfs.h>
+#include <linux/memory_hotplug.h>
 #include <linux/seq_file.h>
 #include <linux/ptdump.h>
 
@@ -370,7 +371,9 @@ bool ptdump_check_wx(void)
 
 static int ptdump_show(struct seq_file *m, void *v)
 {
+       get_online_mems();
        ptdump_walk(m, m->private);
+       put_online_mems();
 
        return 0;
 }