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authorPaul E. McKenney <paulmck@linux.ibm.com>2019-04-14 18:30:22 -0700
committerPaul E. McKenney <paulmck@linux.ibm.com>2019-05-28 09:06:09 -0700
commitab21f6081f7bc09a0918ef888de795d59a907c1a (patch)
treec6a0838e28969de0a8b9a14cecc455634a9e5678 /kernel
parent52b23be7ee023d7f1b67e7a20443ef352c7b5d2d (diff)
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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>
Diffstat (limited to 'kernel')
-rw-r--r--kernel/rcu/rcutorture.c17
1 files changed, 14 insertions, 3 deletions
diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index 6a4558532eac..ef6f6dedf4c4 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -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);