On Wed, Mar 03, 2021 at 04:00:15PM -0800, paulmck@xxxxxxxxxx wrote: > From: "Paul E. McKenney" <paulmck@xxxxxxxxxx> > > 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@xxxxxxxxxxxxx> > Reported-by: Uladzislau Rezki <urezki@xxxxxxxxx> > Cc: Peter Zijlstra <peterz@xxxxxxxxxxxxx> > Cc: Thomas Gleixner <tglx@xxxxxxxxxxxxx> > [ paulmck: Remove unneeded check per Sebastian Siewior feedback. ] > Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxx> Reviewed-by: Frederic Weisbecker <frederic@xxxxxxxxxx>
