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Message-ID: <ZPMK1vcdJ977n89r@gmail.com>
Date: Sat, 2 Sep 2023 12:13:42 +0200
From: Ingo Molnar <mingo@...nel.org>
To: Linus Torvalds <torvalds@...ux-foundation.org>
Cc: linux-kernel@...r.kernel.org, Thomas Gleixner <tglx@...utronix.de>,
Peter Zijlstra <peterz@...radead.org>,
Borislav Petkov <bp@...en8.de>,
Andrew Morton <akpm@...ux-foundation.org>
Subject: [GIT PULL] CPU hotplug fix
Linus,
Please pull the latest smp/urgent git tree from:
git://git.kernel.org/pub/scm/linux/kernel/git/tip/tip.git smp-urgent-2023-09-02
# HEAD: 2b8272ff4a70b866106ae13c36be7ecbef5d5da2 cpu/hotplug: Prevent self deadlock on CPU hot-unplug
Fix a CPU hotplug related deadlock between the task which initiates
and controls a CPU hot-unplug operation vs. the CFS bandwidth timer.
Thanks,
Ingo
------------------>
Thomas Gleixner (1):
cpu/hotplug: Prevent self deadlock on CPU hot-unplug
kernel/cpu.c | 24 +++++++++++++++++++++++-
1 file changed, 23 insertions(+), 1 deletion(-)
diff --git a/kernel/cpu.c b/kernel/cpu.c
index f6811c857102..6de7c6bb74ee 100644
--- a/kernel/cpu.c
+++ b/kernel/cpu.c
@@ -1487,8 +1487,22 @@ static int __ref _cpu_down(unsigned int cpu, int tasks_frozen,
return ret;
}
+struct cpu_down_work {
+ unsigned int cpu;
+ enum cpuhp_state target;
+};
+
+static long __cpu_down_maps_locked(void *arg)
+{
+ struct cpu_down_work *work = arg;
+
+ return _cpu_down(work->cpu, 0, work->target);
+}
+
static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
{
+ struct cpu_down_work work = { .cpu = cpu, .target = target, };
+
/*
* If the platform does not support hotplug, report it explicitly to
* differentiate it from a transient offlining failure.
@@ -1497,7 +1511,15 @@ static int cpu_down_maps_locked(unsigned int cpu, enum cpuhp_state target)
return -EOPNOTSUPP;
if (cpu_hotplug_disabled)
return -EBUSY;
- return _cpu_down(cpu, 0, target);
+
+ /*
+ * Ensure that the control task does not run on the to be offlined
+ * CPU to prevent a deadlock against cfs_b->period_timer.
+ */
+ cpu = cpumask_any_but(cpu_online_mask, cpu);
+ if (cpu >= nr_cpu_ids)
+ return -EBUSY;
+ return work_on_cpu(cpu, __cpu_down_maps_locked, &work);
}
static int cpu_down(unsigned int cpu, enum cpuhp_state target)
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