This is a note to let you know that I've just added the patch titled
arm64: smp: Tell RCU about CPUs that fail to come online
to the 5.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary
The filename of the patch is:
arm64-smp-tell-rcu-about-cpus-that-fail-to-come-onli.patch
and it can be found in the queue-5.4 subdirectory.
If you, or anyone else, feels it should not be added to the stable tree,
please let <stable@xxxxxxxxxxxxxxx> know about it.
commit bede33e3bb3f846c591b05232bf7bcf5a82e1db9
Author: Will Deacon <will@xxxxxxxxxx>
Date: Fri Nov 6 10:25:49 2020 +0000
arm64: smp: Tell RCU about CPUs that fail to come online
[ Upstream commit 04e613ded8c26489b3e0f9101b44462f780d1a35 ]
Commit ce3d31ad3cac ("arm64/smp: Move rcu_cpu_starting() earlier") ensured
that RCU is informed early about incoming CPUs that might end up calling
into printk() before they are online. However, if such a CPU fails the
early CPU feature compatibility checks in check_local_cpu_capabilities(),
then it will be powered off or parked without informing RCU, leading to
an endless stream of stalls:
| rcu: INFO: rcu_preempt detected stalls on CPUs/tasks:
| rcu: 2-O...: (0 ticks this GP) idle=002/1/0x4000000000000000 softirq=0/0 fqs=2593
| (detected by 0, t=5252 jiffies, g=9317, q=136)
| Task dump for CPU 2:
| task:swapper/2 state:R running task stack: 0 pid: 0 ppid: 1 flags:0x00000028
| Call trace:
| ret_from_fork+0x0/0x30
Ensure that the dying CPU invokes rcu_report_dead() prior to being powered
off or parked.
Cc: Qian Cai <cai@xxxxxxxxxx>
Cc: "Paul E. McKenney" <paulmck@xxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Suggested-by: Qian Cai <cai@xxxxxxxxxx>
Link: https://lore.kernel.org/r/20201105222242.GA8842@willie-the-truck
Link: https://lore.kernel.org/r/20201106103602.9849-3-will@xxxxxxxxxx
Signed-off-by: Will Deacon <will@xxxxxxxxxx>
Signed-off-by: Sasha Levin <sashal@xxxxxxxxxx>
diff --git a/arch/arm64/kernel/smp.c b/arch/arm64/kernel/smp.c
index 426409e0d0713..987220ac4cfef 100644
--- a/arch/arm64/kernel/smp.c
+++ b/arch/arm64/kernel/smp.c
@@ -388,6 +388,7 @@ void cpu_die_early(void)
/* Mark this CPU absent */
set_cpu_present(cpu, 0);
+ rcu_report_dead(cpu);
#ifdef CONFIG_HOTPLUG_CPU
update_cpu_boot_status(CPU_KILL_ME);
diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
index 62e59596a30a0..1b1d2b09efa9b 100644
--- a/kernel/rcu/tree.c
+++ b/kernel/rcu/tree.c
@@ -3157,7 +3157,6 @@ void rcu_cpu_starting(unsigned int cpu)
smp_mb(); /* Ensure RCU read-side usage follows above initialization. */
}
-#ifdef CONFIG_HOTPLUG_CPU
/*
* The outgoing function has no further need of RCU, so remove it from
* the rcu_node tree's ->qsmaskinitnext bit masks.
@@ -3197,6 +3196,7 @@ void rcu_report_dead(unsigned int cpu)
per_cpu(rcu_cpu_started, cpu) = 0;
}
+#ifdef CONFIG_HOTPLUG_CPU
/*
* The outgoing CPU has just passed through the dying-idle state, and we
* are being invoked from the CPU that was IPIed to continue the offline
