For kernels built with enable PREEMPT_NONE and CONFIG_DEBUG_ATOMIC_SLEEP,
running the RCU stall tests.

runqemu kvm slirp nographic qemuparams="-m 1024 -smp 4"
bootparams="nokaslr console=ttyS0 rcutorture.stall_cpu=30
rcutorture.stall_no_softlockup=1 rcutorture.stall_cpu_irqsoff=1
rcutorture.stall_cpu_block=1" -d

[   10.841071] rcu-torture: rcu_torture_stall begin CPU stall
[   10.841073] rcu_torture_stall start on CPU 3.
[   10.841077] BUG: scheduling while atomic: rcu_torture_sta/66/0x0000000
....
[   10.841108] Call Trace:
[   10.841110]  <TASK>
[   10.841112]  dump_stack_lvl+0x64/0xb0
[   10.841118]  dump_stack+0x10/0x20
[   10.841121]  __schedule_bug+0x8b/0xb0
[   10.841126]  __schedule+0x2172/0x2940
[   10.841157]  schedule+0x9b/0x150
[   10.841160]  schedule_timeout+0x2e8/0x4f0
[   10.841192]  schedule_timeout_uninterruptible+0x47/0x50
[   10.841195]  rcu_torture_stall+0x2e8/0x300
[   10.841199]  kthread+0x175/0x1a0
[   10.841206]  ret_from_fork+0x2c/0x50

The above calltrace occurs in the local_irq_disable/enable() critical
section call schedule_timeout(), and invoke schedule_timeout() also
implies a quiescent state, of course it also fails to trigger RCU stall,
this commit therefore use mdelay() instead of schedule_timeout() to
trigger RCU stall.

Signed-off-by: Zqiang <qiang1.zhang@intel.com>
---
 kernel/rcu/rcutorture.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
index d06c2da04c34..fe4f5a4074e3 100644
--- a/kernel/rcu/rcutorture.c
+++ b/kernel/rcu/rcutorture.c
@@ -2472,7 +2472,7 @@ static int rcu_torture_stall(void *args)
 #ifdef CONFIG_PREEMPTION
 				preempt_schedule();
 #else
-				schedule_timeout_uninterruptible(HZ);
+				mdelay(HZ);
 #endif
 			} else if (stall_no_softlockup) {
 				touch_softlockup_watchdog();
-- 
2.25.1

On Sun, Mar 19, 2023 at 8:28 PM Zqiang <qiang1.zhang@intel.com> wrote:
>
> For kernels built with enable PREEMPT_NONE and CONFIG_DEBUG_ATOMIC_SLEEP,
> running the RCU stall tests.
>
> runqemu kvm slirp nographic qemuparams="-m 1024 -smp 4"
> bootparams="nokaslr console=ttyS0 rcutorture.stall_cpu=30
> rcutorture.stall_no_softlockup=1 rcutorture.stall_cpu_irqsoff=1
> rcutorture.stall_cpu_block=1" -d
>
> [   10.841071] rcu-torture: rcu_torture_stall begin CPU stall
> [   10.841073] rcu_torture_stall start on CPU 3.
> [   10.841077] BUG: scheduling while atomic: rcu_torture_sta/66/0x0000000
> ....
> [   10.841108] Call Trace:
> [   10.841110]  <TASK>
> [   10.841112]  dump_stack_lvl+0x64/0xb0
> [   10.841118]  dump_stack+0x10/0x20
> [   10.841121]  __schedule_bug+0x8b/0xb0
> [   10.841126]  __schedule+0x2172/0x2940
> [   10.841157]  schedule+0x9b/0x150
> [   10.841160]  schedule_timeout+0x2e8/0x4f0
> [   10.841192]  schedule_timeout_uninterruptible+0x47/0x50
> [   10.841195]  rcu_torture_stall+0x2e8/0x300
> [   10.841199]  kthread+0x175/0x1a0
> [   10.841206]  ret_from_fork+0x2c/0x50
>
> The above calltrace occurs in the local_irq_disable/enable() critical
> section call schedule_timeout(), and invoke schedule_timeout() also
> implies a quiescent state, of course it also fails to trigger RCU stall,
> this commit therefore use mdelay() instead of schedule_timeout() to
> trigger RCU stall.
>
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> ---
>  kernel/rcu/rcutorture.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/rcutorture.c b/kernel/rcu/rcutorture.c
> index d06c2da04c34..fe4f5a4074e3 100644
> --- a/kernel/rcu/rcutorture.c
> +++ b/kernel/rcu/rcutorture.c
> @@ -2472,7 +2472,7 @@ static int rcu_torture_stall(void *args)
>  #ifdef CONFIG_PREEMPTION
>                                 preempt_schedule();
>  #else
> -                               schedule_timeout_uninterruptible(HZ);
> +                               mdelay(HZ);

mdelay accepts milliseconds but HZ is jiffies correct? So this is
broken for systems with HZ != 1000.

So you need to call mdelay(jiffies_to_msecs(HZ)) instead.

 - Joel