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The ptdump code can race with concurrent modifications of the > kernel page tables. When leaf entries are modified concurrently, the dump > code may log stale or inconsistent information for a VA range, but this is > otherwise not harmful. > > But when intermediate levels of kernel page table are freed, the dump code > will continue to use memory that has been freed and potentially reallocated > for another purpose. In such cases, the ptdump code may dereference bogus > addresses, leading to a number of potential problems. > > To avoid the above mentioned race condition, platforms such as arm64, riscv > and s390 take memory hotplug lock, while dumping kernel page table via the > sysfs interface /sys/kernel/debug/kernel_page_tables. > > Similar race condition exists while checking for pages that might have been > marked W+X via /sys/kernel/debug/kernel_page_tables/check_wx_pages which in > turn calls ptdump_check_wx(). Instead of solving this race condition again, > let's just move the memory hotplug lock inside generic ptdump_check_wx() > which will benefit both the scenarios. > > Drop get_online_mems() and put_online_mems() combination from all existing > platform ptdump code paths. > > Cc: Catalin Marinas > Cc: Will Deacon > Cc: Ryan Roberts > Cc: Paul Walmsley > Cc: Palmer Dabbelt > Cc: Alexander Gordeev > Cc: Gerald Schaefer > Cc: Heiko Carstens > Cc: Vasily Gorbik > Cc: Christian Borntraeger > Cc: Sven Schnelle > Cc: Andrew Morton > CC: linux-arm-kernel@lists.infradead.org > Cc: linux-kernel@vger.kernel.org > Cc: linux-riscv@lists.infradead.org > Cc: linux-s390@vger.kernel.org > Cc: linux-mm@kvack.org > Signed-off-by: Anshuman Khandual > --- Reviewed-by: Dev Jain