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Message-ID: <ZbqfMR_mVLaSCj4Q@carbonx1>
Date: Wed, 31 Jan 2024 20:27:45 +0100
From: Helge Deller <deller@...nel.org>
To: Tejun Heo <tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>,
linux-kernel@...r.kernel.org
Cc: linux-parisc@...r.kernel.org
Subject: [PATCH][RFC] workqueue: Fix kernel panic on CPU hot-unplug
When hot-unplugging a 32-bit CPU on the parisc platform with
"chcpu -d 1", I get the following kernel panic. Adding a check
for !pwq prevents the panic.
Kernel Fault: Code=26 (Data memory access rights trap) at addr 00000000
CPU: 1 PID: 21 Comm: cpuhp/1 Not tainted 6.8.0-rc1-32bit+ #1291
Hardware name: 9000/778/B160L
IASQ: 00000000 00000000 IAOQ: 10446db4 10446db8
IIR: 0f80109c ISR: 00000000 IOR: 00000000
CPU: 1 CR30: 11dd1710 CR31: 00000000
IAOQ[0]: wq_update_pod+0x98/0x14c
IAOQ[1]: wq_update_pod+0x9c/0x14c
RP(r2): wq_update_pod+0x80/0x14c
Backtrace:
[<10448744>] workqueue_offline_cpu+0x1d4/0x1dc
[<10429db4>] cpuhp_invoke_callback+0xf8/0x200
[<1042a1d0>] cpuhp_thread_fun+0xb8/0x164
[<10452970>] smpboot_thread_fn+0x284/0x288
[<1044d8f4>] kthread+0x12c/0x13c
[<1040201c>] ret_from_kernel_thread+0x1c/0x24
Kernel panic - not syncing: Kernel Fault
Signed-off-by: Helge Deller <deller@....de>
---
diff --git a/kernel/workqueue.c b/kernel/workqueue.c
index 76e60faed892..dfeee7b7322c 100644
--- a/kernel/workqueue.c
+++ b/kernel/workqueue.c
@@ -4521,6 +4521,8 @@ static void wq_update_pod(struct workqueue_struct *wq, int cpu,
wq_calc_pod_cpumask(target_attrs, cpu, off_cpu);
pwq = rcu_dereference_protected(*per_cpu_ptr(wq->cpu_pwq, cpu),
lockdep_is_held(&wq_pool_mutex));
+ if (!pwq)
+ return;
if (wqattrs_equal(target_attrs, pwq->pool->attrs))
return;
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