+ vmstat-disable-vmstat_work-on-vmstat_cpu_down_prep.patch added to mm-hotfixes-unstable branch

[Andrew Morton <akpm@linux-foundation.org>]

The patch titled
     Subject: vmstat: disable vmstat_work on vmstat_cpu_down_prep()
has been added to the -mm mm-hotfixes-unstable branch.  Its filename is
     vmstat-disable-vmstat_work-on-vmstat_cpu_down_prep.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/vmstat-disable-vmstat_work-on-vmstat_cpu_down_prep.patch

This patch will later appear in the mm-hotfixes-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: Koichiro Den <koichiro.den@canonical.com>
Subject: vmstat: disable vmstat_work on vmstat_cpu_down_prep()
Date: Fri, 20 Dec 2024 22:42:34 +0900

Even after mm/vmstat:online teardown, shepherd may still queue work for
the dying cpu until the cpu is removed from online mask.  While it's quite
rare, this means that after unbind_workers() unbinds a per-cpu kworker, it
potentially runs vmstat_update for the dying CPU on an irrelevant cpu
before entering STARTING section.  When CONFIG_DEBUG_PREEMPT=y, it results
in the following error with the backtrace.

  BUG: using smp_processor_id() in preemptible [00000000] code: \
                                               kworker/7:3/1702
  caller is refresh_cpu_vm_stats+0x235/0x5f0
  CPU: 0 UID: 0 PID: 1702 Comm: kworker/7:3 Tainted: G
  Tainted: [N]=TEST
  Workqueue: mm_percpu_wq vmstat_update
  Call Trace:
   <TASK>
   dump_stack_lvl+0x8d/0xb0
   check_preemption_disabled+0xce/0xe0
   refresh_cpu_vm_stats+0x235/0x5f0
   vmstat_update+0x17/0xa0
   process_one_work+0x869/0x1aa0
   worker_thread+0x5e5/0x1100
   kthread+0x29e/0x380
   ret_from_fork+0x2d/0x70
   ret_from_fork_asm+0x1a/0x30
   </TASK>

So, disable vmstat_work reliably on vmstat_cpu_down_prep().

Link: https://lkml.kernel.org/r/20241220134234.3809621-1-koichiro.den@canonical.com
Signed-off-by: Koichiro Den <koichiro.den@canonical.com>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: <stable@vger.kernel.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

 mm/vmstat.c |    2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/mm/vmstat.c~vmstat-disable-vmstat_work-on-vmstat_cpu_down_prep
+++ a/mm/vmstat.c
@@ -2154,7 +2154,7 @@ static int vmstat_cpu_online(unsigned in
 
 static int vmstat_cpu_down_prep(unsigned int cpu)
 {
-	cancel_delayed_work_sync(&per_cpu(vmstat_work, cpu));
+	disable_delayed_work_sync(&per_cpu(vmstat_work, cpu));
 	return 0;
 }
 
_

Patches currently in -mm which might be from koichiro.den@canonical.com are

vmstat-disable-vmstat_work-on-vmstat_cpu_down_prep.patch
hugetlb-prioritize-surplus-allocation-from-current-node.patch