[PATCH 4.18 085/171] memory_hotplug: cond_resched in __remove_pages

[Greg Kroah-Hartman]

4.18-stable review patch.  If anyone has any objections, please let me know.

------------------

From: Michal Hocko <mhocko@xxxxxxxx>

commit dd33ad7b251f900481701b2a82d25de583867708 upstream.

We have received a bug report that unbinding a large pmem (>1TB) can
result in a soft lockup:

  NMI watchdog: BUG: soft lockup - CPU#9 stuck for 23s! [ndctl:4365]
  [...]
  Supported: Yes
  CPU: 9 PID: 4365 Comm: ndctl Not tainted 4.12.14-94.40-default #1 SLE12-SP4
  Hardware name: Intel Corporation S2600WFD/S2600WFD, BIOS SE5C620.86B.01.00.0833.051120182255 05/11/2018
  task: ffff9cce7d4410c0 task.stack: ffffbe9eb1bc4000
  RIP: 0010:__put_page+0x62/0x80
  Call Trace:
   devm_memremap_pages_release+0x152/0x260
   release_nodes+0x18d/0x1d0
   device_release_driver_internal+0x160/0x210
   unbind_store+0xb3/0xe0
   kernfs_fop_write+0x102/0x180
   __vfs_write+0x26/0x150
   vfs_write+0xad/0x1a0
   SyS_write+0x42/0x90
   do_syscall_64+0x74/0x150
   entry_SYSCALL_64_after_hwframe+0x3d/0xa2
  RIP: 0033:0x7fd13166b3d0

It has been reported on an older (4.12) kernel but the current upstream
code doesn't cond_resched in the hot remove code at all and the given
range to remove might be really large.  Fix the issue by calling
cond_resched once per memory section.

Link: http://lkml.kernel.org/r/20181031125840.23982-1-mhocko@xxxxxxxxxx
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Johannes Thumshirn <jthumshirn@xxxxxxx>
Cc: Dan Williams <dan.j.williams@xxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxxxxxxxxxxxxxx>

---
 mm/memory_hotplug.c |    1 +
 1 file changed, 1 insertion(+)

--- a/mm/memory_hotplug.c
+++ b/mm/memory_hotplug.c
@@ -587,6 +587,7 @@ int __remove_pages(struct zone *zone, un
 	for (i = 0; i < sections_to_remove; i++) {
 		unsigned long pfn = phys_start_pfn + i*PAGES_PER_SECTION;
 
+		cond_resched();
 		ret = __remove_section(zone, __pfn_to_section(pfn), map_offset,
 				altmap);
 		map_offset = 0;