[PATCH v3 1/4] rcutorture: Don't disable softirqs with preemption disabled when PREEMPT_RT

From: Valentin Schneider
Date: Wed Aug 11 2021 - 16:14:21 EST


Running RCU torture with CONFIG_PREEMPT_RT under v5.14-rc4-rt6 triggers:

[ 8.755472] DEBUG_LOCKS_WARN_ON(this_cpu_read(softirq_ctrl.cnt))
[ 8.755482] WARNING: CPU: 1 PID: 137 at kernel/softirq.c:172 __local_bh_disable_ip (kernel/softirq.c:172 (discriminator 31))
[ 8.755500] Modules linked in:
[ 8.755506] CPU: 1 PID: 137 Comm: rcu_torture_rea Not tainted 5.14.0-rc4-rt6 #171
[ 8.755514] Hardware name: ARM Juno development board (r0) (DT)
[ 8.755518] pstate: 60000005 (nZCv daif -PAN -UAO -TCO BTYPE=--)
[ 8.755622] Call trace:
[ 8.755624] __local_bh_disable_ip (kernel/softirq.c:172 (discriminator 31))
[ 8.755633] rcutorture_one_extend (kernel/rcu/rcutorture.c:1453)
[ 8.755640] rcu_torture_one_read (kernel/rcu/rcutorture.c:1601 kernel/rcu/rcutorture.c:1645)
[ 8.755645] rcu_torture_reader (kernel/rcu/rcutorture.c:1737)
[ 8.755650] kthread (kernel/kthread.c:327)
[ 8.755656] ret_from_fork (arch/arm64/kernel/entry.S:783)
[ 8.755663] irq event stamp: 11959
[ 8.755666] hardirqs last enabled at (11959): __rcu_read_unlock (kernel/rcu/tree_plugin.h:695 kernel/rcu/tree_plugin.h:451)
[ 8.755675] hardirqs last disabled at (11958): __rcu_read_unlock (kernel/rcu/tree_plugin.h:661 kernel/rcu/tree_plugin.h:451)
[ 8.755683] softirqs last enabled at (11950): __local_bh_enable_ip (./arch/arm64/include/asm/irqflags.h:85 kernel/softirq.c:261)
[ 8.755692] softirqs last disabled at (11942): rcutorture_one_extend (./include/linux/bottom_half.h:19 kernel/rcu/rcutorture.c:1441)

Per this warning, softirqs cannot be disabled in a non-preemptible region
under CONFIG_PREEMPT_RT. Adjust RCU torture accordingly.

Signed-off-by: Valentin Schneider <valentin.schneider@xxxxxxx>
---
kernel/rcu/rcutorture.c | 2 ++
1 file changed, 2 insertions(+)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index eecd1caef71d..4f3db1d3170d 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -1548,6 +1548,8 @@ rcutorture_extend_mask(int oldmask, struct torture_random_state *trsp)
* them on non-RT.
*/
if (IS_ENABLED(CONFIG_PREEMPT_RT)) {
+ /* Can't disable bh in atomic context under PREEMPT_RT */
+ mask &= ~(RCUTORTURE_RDR_ATOM_BH | RCUTORTURE_RDR_ATOM_RBH);
/*
* Can't release the outermost rcu lock in an irq disabled
* section without preemption also being disabled, if irqs
--
2.25.1