From: Paul E. McKenney Date: Sat, 13 Feb 2021 00:20:40 +0000 (-0800) Subject: softirq: Don't try waking ksoftirqd before it has been spawned X-Git-Url: http://git.maquefel.me/?a=commitdiff_plain;h=1c0c4bc1ceb580851b2d76fdef9712b3bdae134b;p=linux.git softirq: Don't try waking ksoftirqd before it has been spawned 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 Reported-by: Uladzislau Rezki Cc: Peter Zijlstra Cc: Thomas Gleixner [ paulmck: Remove unneeded check per Sebastian Siewior feedback. ] Reviewed-by: Frederic Weisbecker Signed-off-by: Paul E. McKenney --- diff --git a/kernel/softirq.c b/kernel/softirq.c index 9908ec4a9bfed..bad14ca2b5200 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -211,7 +211,7 @@ static inline void invoke_softirq(void) if (ksoftirqd_running(local_softirq_pending())) return; - if (!force_irqthreads) { + if (!force_irqthreads || !__this_cpu_read(ksoftirqd)) { #ifdef CONFIG_HAVE_IRQ_EXIT_ON_IRQ_STACK /* * We can safely execute softirq on the current stack if