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@xxxxxxxxxxxxx>
Subject: vmstat: disable vmstat_work on vmstat_cpu_down_prep()
Date: Sat, 21 Dec 2024 12:33:20 +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 atomic AP states. 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, for mm/vmstat:online, disable vmstat_work reliably on teardown and
symmetrically enable it on startup.
Link: https://lkml.kernel.org/r/20241221033321.4154409-1-koichiro.den@xxxxxxxxxxxxx
Signed-off-by: Koichiro Den <koichiro.den@xxxxxxxxxxxxx>
Cc: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Cc: <stable@xxxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/vmstat.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
--- a/mm/vmstat.c~vmstat-disable-vmstat_work-on-vmstat_cpu_down_prep
+++ a/mm/vmstat.c
@@ -2148,13 +2148,14 @@ static int vmstat_cpu_online(unsigned in
if (!node_state(cpu_to_node(cpu), N_CPU)) {
node_set_state(cpu_to_node(cpu), N_CPU);
}
+ enable_delayed_work(&per_cpu(vmstat_work, cpu));
return 0;
}
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@xxxxxxxxxxxxx are
vmstat-disable-vmstat_work-on-vmstat_cpu_down_prep.patch
hugetlb-prioritize-surplus-allocation-from-current-node.patch
