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rcutorture: Make {,s}rcu_read_delay() better handle forward-progress testing

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The rcu_read_delay() and srcu_read_delay() functions are suppose to
avoid (or at least to minimize) read-side delays during call_rcu()-based
forward-progress testing.  Although rcu_read_delay() does account for
this by testing rcu_fwd_cb_nodelay, it only does so in some cases, and
srcu_read_delay() does not bother at all.  And rcutorture testing does
occasionally turn up the MIN_FWD_CBS_LAUNDERED failure when running
forward-progress tests on Tree SRCU flavors.

This commit therefore makes both rcu_read_delay() and srcu_read_delay()
take an immediate exit if rcu_fwd_cb_nodelay is set.

Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
This commit is contained in:
Paul E. McKenney 2026-07-28 14:58:49 -07:00
parent 6c22d64011
commit 20ed97cfde
1 changed files with 11 additions and 5 deletions
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16
kernel/rcu/rcutorture.c
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@ -469,12 +469,14 @@ rcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
unsigned long longdelay_ms = 300;
unsigned long long ts;
/* We want a short delay sometimes to make a reader delay the grace
* period, and we want a long delay occasionally to trigger
* force_quiescent_state. */
// If there is a forward-progress test in flight, don't delay.
if (atomic_read(&rcu_fwd_cb_nodelay))
return;
if (!atomic_read(&rcu_fwd_cb_nodelay) &&
!(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {
// We want a short delay sometimes to make a reader delay the grace
// period, and we want a long delay occasionally to trigger
// force_quiescent_state.
if (!(torture_random(rrsp) % (nrealreaders * 2000 * longdelay_ms))) {
started = cur_ops->get_gp_seq();
ts = rcu_trace_clock_local();
if ((preempt_count() & HARDIRQ_MASK) || softirq_count())
@ -766,6 +768,10 @@ srcu_read_delay(struct torture_random_state *rrsp, struct rt_read_seg *rtrsp)
const long uspertick = 1000000 / HZ;
const long longdelay = 10;
// If there is a forward-progress test in flight, don't delay.
if (atomic_read(&rcu_fwd_cb_nodelay))
return;
// We want there to be long-running readers, but not all the time.
// The !rcu_preempt_depth() is for RCU Tasks Trace.