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

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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>
This commit is contained in:
Paul E. McKenney 2019-04-14 18:30:22 -07:00
parent 52b23be7ee
commit ab21f6081f
1 changed files with 14 additions and 3 deletions
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17
kernel/rcu/rcutorture.c
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@ -1667,6 +1667,17 @@ static void rcu_torture_fwd_cb_cr(struct rcu_head *rhp)
spin_unlock_irqrestore(&rcu_fwd_lock, flags); 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 * Free all callbacks on the rcu_fwd_cb_head list, either because the
* test is over or because we hit an OOM event. * 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); spin_unlock_irqrestore(&rcu_fwd_lock, flags);
kfree(rfcp); kfree(rfcp);
freed++; freed++;
cond_resched(); rcu_torture_fwd_prog_cond_resched();
} }
return freed; return freed;
} }
@ -1734,7 +1745,7 @@ static void rcu_torture_fwd_prog_nr(int *tested, int *tested_tries)
udelay(10); udelay(10);
cur_ops->readunlock(idx); cur_ops->readunlock(idx);
if (!fwd_progress_need_resched || need_resched()) if (!fwd_progress_need_resched || need_resched())
cond_resched(); rcu_torture_fwd_prog_cond_resched();
} }
(*tested_tries)++; (*tested_tries)++;
if (!time_before(jiffies, stopat) && if (!time_before(jiffies, stopat) &&
@ -1817,7 +1828,7 @@ static void rcu_torture_fwd_prog_cr(void)
rfcp->rfc_gps = 0; rfcp->rfc_gps = 0;
} }
cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr); cur_ops->call(&rfcp->rh, rcu_torture_fwd_cb_cr);
cond_resched(); rcu_torture_fwd_prog_cond_resched();
} }
stoppedat = jiffies; stoppedat = jiffies;
n_launders_cb_snap = READ_ONCE(n_launders_cb); n_launders_cb_snap = READ_ONCE(n_launders_cb);