rcutorture: Give the scheduler a chance on PREEMPT && NO_HZ_FULL kernels (ab21f608) · Commits · 戴 / test

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>

kernel/rcu/rcutorture.c

+14 −3

Original line number	Diff line number	Diff line
		@@ -1667,6 +1667,17 @@ static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)
		spin_unlock_irqrestore(&rcu_fwd_lock, flags);
		}

		// Give the scheduler a chance, even on nohz_full CPUs.
		static void rcu_torture_fwd_prog_cond_resched(void)
		{
		if (IS_ENABLED(CONFIG_PREEMPT) && IS_ENABLED(CONFIG_NO_HZ_FULL)) {
		if (need_resched())
		schedule();
		} else {
		cond_resched();
		}
		}

		/*
		* Free all callbacks on the rcu_fwd_cb_head list, either because the
		* test is over or because we hit an OOM event.
		@@ -1690,7 +1701,7 @@ static unsigned long rcu_torture_fwd_prog_cbfree(void)
		spin_unlock_irqrestore(&rcu_fwd_lock, flags);
		kfree(rfcp);
		freed++;
		cond_resched();
		rcu_torture_fwd_prog_cond_resched();
		}
		return freed;
		}
		@@ -1734,7 +1745,7 @@ static void rcu_torture_fwd_prog_nr(int tested, int tested_tries)
		udelay(10);
		cur_ops->readunlock(idx);
		if (!fwd_progress_need_resched \|\| need_resched())
		cond_resched();
		rcu_torture_fwd_prog_cond_resched();
		}
		(*tested_tries)++;
		if (!time_before(jiffies, stopat) &&
		@@ -1817,7 +1828,7 @@ static void rcu_torture_fwd_prog_cr(void)
		rfcp->rfc_gps = 0;
		}
		cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr);
		cond_resched();
		rcu_torture_fwd_prog_cond_resched();
		}
		stoppedat = jiffies;
		n_launders_cb_snap = READ_ONCE(n_launders_cb);

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