Patch "x86/mm/ptdump: Fix soft lockup in page table walker" has been added to the 4.9-stable tree

This is a note to let you know that I've just added the patch titled

x86/mm/ptdump: Fix soft lockup in page table walker

to the 4.9-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-mm-ptdump-fix-soft-lockup-in-page-table-walker.patch
and it can be found in the queue-4.9 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

From: Andrey Ryabinin <[email protected]>
Date: Fri, 10 Feb 2017 12:54:05 +0300
Subject: x86/mm/ptdump: Fix soft lockup in page table walker

From: Andrey Ryabinin <[email protected]>

commit 146fbb766934dc003fcbf755b519acef683576bf upstream.

CONFIG_KASAN=y needs a lot of virtual memory mapped for its shadow. In that case ptdump_walk_pgd_level_core() takes a lot of time to walk across all page tables and doing this without
a rescheduling causes soft lockups:

NMI watchdog: BUG: soft lockup - CPU#3 stuck for 23s! [swapper/0:1]
...

 Call Trace:
  ptdump_walk_pgd_level_core+0x40c/0x550
  ptdump_walk_pgd_level_checkwx+0x17/0x20
  mark_rodata_ro+0x13b/0x150
  kernel_init+0x2f/0x120
  ret_from_fork+0x2c/0x40

I guess that this issue might arise even without KASAN on huge machines with several terabytes of RAM.

Stick cond_resched() in pgd loop to fix this.

---
 arch/x86/mm/dump_pagetables.c |    2 ++
 1 file changed, 2 insertions(+)

@@ -15,6 +15,7 @@
 #include <linux/debugfs.h>
 #include <linux/mm.h>
 #include <linux/init.h>
+#include <linux/sched.h>
 #include <linux/seq_file.h>
 
 #include <asm/pgtable.h>

@@ -406,6 +407,7 @@ static void ptdump_walk_pgd_level_core(s
 		} else
 			note_page(m, &st, __pgprot(0), 1);
 
+		cond_resched();
 		start++;
 	}
 

Patches currently in stable-queue which might be from [email protected] are

queue-4.9/x86-mm-ptdump-fix-soft-lockup-in-page-table-walker.patch queue-4.9/drm-i915-fix-use-after-free-in-page_flip_completed.patch