tree c6a0838e28969de0a8b9a14cecc455634a9e5678
parent 52b23be7ee023d7f1b67e7a20443ef352c7b5d2d
author Paul E. McKenney <paulmck@linux.ibm.com> 1555291822 -0700
committer Paul E. McKenney <paulmck@linux.ibm.com> 1559059569 -0700

rcutorture: Give the scheduler a chance on PREEMPT && NO_HZ_FULL kernels

In !PREEMPT kernels, cond_resched() is a no-op.  In NO_HZ_FULL kernels,
in-kernel execution (such as that of rcutorture's kthreads) might extend
indefinitely without the scheduler gaining the aid of a scheduling-clock
interrupt.  This combination can make the interaction of an rcutorture
forward-progress test and a CPU-hotplug stop_machine operation make less
forward progress than one might like.  Additionally, Sebastian Siewior
notes that NO_HZ_FULL kernels have a scheduler check upon return to
userspace execution, which suggests that in-kernel emulation of tight
userspace loops containing system calls doing call_rcu() might also need
explicit checks in the PREEMPT && NO_HZ_FULL case.

This commit therefore introduces a rcu_torture_fwd_prog_cond_resched()
function that explicitly invokes schedule() in such kernels whenever
need_resched() returns true, while retaining use of cond_resched()
for kernels that are either !PREEMPT or !NO_HZ_FULL.

Signed-off-by: Paul E. McKenney <paulmck@linux.ibm.com>