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In-Reply-To: <20230320003316.3897447-1-qiang1.zhang@intel.com>
From:   Joel Fernandes <joel@joelfernandes.org>
Date:   Sun, 19 Mar 2023 22:58:08 -0400
Message-ID: <CAEXW_YSCXhgeSgvf=HnoQDrT8T1F7q8m=dobEYHanXjnSUmCHw@mail.gmail.com>
Subject: Re: [PATCH] rcutorture: Convert schedule_timeout_uninterruptible() to
 mdelay() in rcu_torture_stall()
To:     Zqiang <qiang1.zhang@intel.com>
Cc:     paulmck@kernel.org, frederic@kernel.org, rcu@vger.kernel.org,
        linux-kernel@vger.kernel.org
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On Sun, Mar 19, 2023 at 8:28=E2=80=AFPM Zqiang <qiang1.zhang@intel.com> wro=
te:
>
> For kernels built with enable PREEMPT_NONE and CONFIG_DEBUG_ATOMIC_SLEEP,
> running the RCU stall tests.
>
> runqemu kvm slirp nographic qemuparams=3D"-m 1024 -smp 4"
> bootparams=3D"nokaslr console=3DttyS0 rcutorture.stall_cpu=3D30
> rcutorture.stall_no_softlockup=3D1 rcutorture.stall_cpu_irqsoff=3D1
> rcutorture.stall_cpu_block=3D1" -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 !=3D 1000.

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

 - Joel