[PATCH 7/8] refscale: Do not diable interrupts for tests involving local_bh_enable()

[Paul E. McKenney]

Some kernel configurations prohibit invoking local_bh_enable() while
interrupts are disabled.  However, refscale disables interrupts to reduce
OS noise during the tests, which results in splats.  This commit therefore
adds an ->enable_irqs flag to the ref_scale_ops structure, and refrains
from disabling interrupts when that flag is set.  This flag is set for
the "bh" and "incpercpubh" scale_type module-parameter values.

Signed-off-by: Paul E. McKenney <paul...@kernel.org>
---
 kernel/rcu/refscale.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/rcu/refscale.c b/kernel/rcu/refscale.c
index 2b247355de40..7429ec9f0092 100644
--- a/kernel/rcu/refscale.c
+++ b/kernel/rcu/refscale.c
@@ -136,6 +136,7 @@ struct ref_scale_ops {
        void (*cleanup)(void);
        void (*readsection)(const int nloops);
        void (*delaysection)(const int nloops, const int udl, const int ndl);
+       bool enable_irqs;
        const char *name;
 };
 
@@ -495,6 +496,7 @@ static const struct ref_scale_ops incpercpubh_ops = {
        .init           = rcu_sync_scale_init,
        .readsection    = ref_incpercpubh_section,
        .delaysection   = ref_incpercpubh_delay_section,
+       .enable_irqs    = true,
        .name           = "incpercpubh"
 };
 
@@ -872,6 +874,7 @@ static void ref_bh_delay_section(const int nloops, const 
int udl, const int ndl)
 static const struct ref_scale_ops bh_ops = {
        .readsection    = ref_bh_section,
        .delaysection   = ref_bh_delay_section,
+       .enable_irqs    = true,
        .name           = "bh"
 };
 
@@ -1234,15 +1237,18 @@ ref_scale_reader(void *arg)
        if (!atomic_dec_return(&n_warmedup))
                while (atomic_read_acquire(&n_warmedup))
                        rcu_scale_one_reader();
-       // Also keep interrupts disabled.  This also has the effect
-       // of preventing entries into slow path for rcu_read_unlock().
-       local_irq_save(flags);
+       // Also keep interrupts disabled when it is safe to do so, which
+       // it is not for local_bh_enable().  This also has the effect of
+       // preventing entries into slow path for rcu_read_unlock().
+       if (!cur_ops->enable_irqs)
+               local_irq_save(flags);
        start = ktime_get_mono_fast_ns();
 
        rcu_scale_one_reader();
 
        duration = ktime_get_mono_fast_ns() - start;
-       local_irq_restore(flags);
+       if (!cur_ops->enable_irqs)
+               local_irq_restore(flags);
 
        rt->last_duration_ns = WARN_ON_ONCE(duration < 0) ? 0 : duration;
        // To reduce runtime-skew noise, do maintain-load invocations until
-- 
2.40.1