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SubjectRe: [PATCH tip/core/rcu 06/10] softirq: Don't try waking ksoftirqd before it has been spawned
On Wed, Mar 03, 2021 at 04:00:15PM -0800, paulmck@kernel.org wrote:
> From: "Paul E. McKenney" <paulmck@kernel.org>
>
> If there is heavy softirq activity, the softirq system will attempt
> to awaken ksoftirqd and will stop the traditional back-of-interrupt
> softirq processing. This is all well and good, but only if the
> ksoftirqd kthreads already exist, which is not the case during early
> boot, in which case the system hangs.
>
> One reproducer is as follows:
>
> tools/testing/selftests/rcutorture/bin/kvm.sh --allcpus --duration 2 --configs "TREE03" --kconfig "CONFIG_DEBUG_LOCK_ALLOC=y CONFIG_PROVE_LOCKING=y CONFIG_NO_HZ_IDLE=y CONFIG_HZ_PERIODIC=n" --bootargs "threadirqs=1" --trust-make
>
> This commit therefore adds a couple of existence checks for ksoftirqd
> and forces back-of-interrupt softirq processing when ksoftirqd does not
> yet exist. With this change, the above test passes.
>
> Reported-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
> Reported-by: Uladzislau Rezki <urezki@gmail.com>
> Cc: Peter Zijlstra <peterz@infradead.org>
> Cc: Thomas Gleixner <tglx@linutronix.de>
> [ paulmck: Remove unneeded check per Sebastian Siewior feedback. ]
> Signed-off-by: Paul E. McKenney <paulmck@kernel.org>

Reviewed-by: Frederic Weisbecker <frederic@kernel.org>

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