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...

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.co... 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