s390/mm,ptdump: hold memory hotplug lock while walking for kernel page table dump

This is the s390 variant of commit bf2b59f60ee1 ("arm64/mm: Hold
memory hotplug lock while walking for kernel page table dump").

Right now this doesn't fix any real bug, however as soon as kvm
patches get merged which make use of memory remove we might end up
dereferencing/accessing freed page tables.

Therefore fix this potential bug already now.

Reviewed-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

diff --git a/arch/s390/mm/dump_pagetables.c b/arch/s390/mm/dump_pagetables.c
index 93a29e2..3c5e405 100644 (file)
--- a/arch/s390/mm/dump_pagetables.c
+++ b/arch/s390/mm/dump_pagetables.c
@@ -129,7 +129,9 @@ static int ptdump_show(struct seq_file *m, void *v)
                .marker = address_markers,
        };
 
+       get_online_mems();
        ptdump_walk_pgd(&st.ptdump, &init_mm, NULL);
+       put_online_mems();
        return 0;
 }
 DEFINE_SHOW_ATTRIBUTE(ptdump);