2023-03-20 00:28:48

by Zqiang

Subject: [PATCH] rcutorture: Convert schedule_timeout_uninterruptible() to mdelay() in rcu_torture_stall()

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 <[email protected]>
---
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

2023-03-20 02:58:26

by Joel Fernandes

Subject: Re: [PATCH] rcutorture: Convert schedule_timeout_uninterruptible() to mdelay() in rcu_torture_stall()

On Sun, Mar 19, 2023 at 8:28 PM Zqiang <[email protected]> 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 <[email protected]>
> ---
> 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