Patch "PM/hibernate: touch NMI watchdog when creating snapshot" has been added to the 4.12-stable tree

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

PM/hibernate: touch NMI watchdog when creating snapshot

to the 4.12-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:
pm-hibernate-touch-nmi-watchdog-when-creating-snapshot.patch
and it can be found in the queue-4.12 subdirectory.

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

From: Chen Yu <[email protected]>
Date: Fri, 25 Aug 2017 15:55:30 -0700
Subject: PM/hibernate: touch NMI watchdog when creating snapshot

From: Chen Yu <[email protected]>

commit 556b969a1cfe2686aae149137fa1dfcac0eefe54 upstream.

There is a problem that when counting the pages for creating the hibernation snapshot will take significant amount of time, especially on system with large memory. Since the counting job is performed with irq disabled, this might lead to NMI lockup. The following warning were found on a system with 1.5TB DRAM:

Freezing user space processes ... (elapsed 0.002 seconds) done. OOM killer disabled.
PM: Preallocating image memory...
NMI watchdog: Watchdog detected hard LOCKUP on cpu 27

  CPU: 27 PID: 3128 Comm: systemd-sleep Not tainted 4.13.0-0.rc2.git0.1.fc27.x86_64 #1
  task: ffff9f01971ac000 task.stack: ffffb1a3f325c000
  RIP: 0010:memory_bm_find_bit+0xf4/0x100
  Call Trace:
   swsusp_set_page_free+0x2b/0x30
   mark_free_pages+0x147/0x1c0
   count_data_pages+0x41/0xa0
   hibernate_preallocate_memory+0x80/0x450
   hibernation_snapshot+0x58/0x410
   hibernate+0x17c/0x310
   state_store+0xdf/0xf0
   kobj_attr_store+0xf/0x20
   sysfs_kf_write+0x37/0x40
   kernfs_fop_write+0x11c/0x1a0
   __vfs_write+0x37/0x170
   vfs_write+0xb1/0x1a0
   SyS_write+0x55/0xc0
   entry_SYSCALL_64_fastpath+0x1a/0xa5
  ...
  done (allocated 6590003 pages)
  PM: Allocated 26360012 kbytes in 19.89 seconds (1325.28 MB/s)

It has taken nearly 20 seconds(2.10GHz CPU) thus the NMI lockup was triggered. In case the timeout of the NMI watch dog has been set to 1 second, a safe interval should be 6590003/20 = 320k pages in theory. However there might also be some platforms running at a lower frequency, so feed the watchdog every 100k pages.

---
 mm/page_alloc.c |   20 ++++++++++++++++++--
 1 file changed, 18 insertions(+), 2 deletions(-)

@@ -66,6 +66,7 @@
 #include <linux/kthread.h>
 #include <linux/memcontrol.h>
 #include <linux/ftrace.h>
+#include <linux/nmi.h>
 
 #include <asm/sections.h>
 #include <asm/tlbflush.h>

@@ -2495,9 +2496,14 @@ void drain_all_pages(struct zone *zone)
 
 #ifdef CONFIG_HIBERNATION
 
+/*
+ * Touch the watchdog for every WD_PAGE_COUNT pages.
+ */
+#define WD_PAGE_COUNT	(128*1024)
+
 void mark_free_pages(struct zone *zone)
 {
-	unsigned long pfn, max_zone_pfn;
+	unsigned long pfn, max_zone_pfn, page_count = WD_PAGE_COUNT;
 	unsigned long flags;
 	unsigned int order, t;
 	struct page *page;

@@ -2512,6 +2518,11 @@ void mark_free_pages(struct zone *zone)
 		if (pfn_valid(pfn)) {
 			page = pfn_to_page(pfn);
 
+			if (!--page_count) {
+				touch_nmi_watchdog();
+				page_count = WD_PAGE_COUNT;
+			}
+
 			if (page_zone(page) != zone)
 				continue;
 

@@ -2525,8 +2536,13 @@ void mark_free_pages(struct zone *zone)
 			unsigned long i;
 
 			pfn = page_to_pfn(page);
-			for (i = 0; i < (1UL << order); i++)
+			for (i = 0; i < (1UL << order); i++) {
+				if (!--page_count) {
+					touch_nmi_watchdog();
+					page_count = WD_PAGE_COUNT;
+				}
 				swsusp_set_page_free(pfn_to_page(pfn + i));
+			}
 		}
 	}
 	spin_unlock_irqrestore(&zone->lock, flags);

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

queue-4.12/pm-hibernate-touch-nmi-watchdog-when-creating-snapshot.patch