From: Joel Fernandes <joel@joelfernandes.org>
To: Zqiang <qiang1.zhang@intel.com>
Cc: paulmck@kernel.org, frederic@kernel.org,
quic_neeraju@quicinc.com, rcu@vger.kernel.org,
linux-kernel@vger.kernel.org
Subject: Re: [PATCH] rcu: Fix use __this_cpu_read() warning in preemptible code
Date: Thu, 13 Oct 2022 15:39:45 +0000 [thread overview]
Message-ID: <Y0gxQQzLdJLOp7wI@google.com> (raw)
In-Reply-To: <20221013044148.2894320-1-qiang1.zhang@intel.com>
On Thu, Oct 13, 2022 at 12:41:48PM +0800, Zqiang wrote:
> BUG: using __this_cpu_read() in preemptible [00000000]
> code: rcu_torture_fqs/398
> caller is __this_cpu_preempt_check+0x13/0x20
> CPU: 3 PID: 398 Comm: rcu_torture_fqs Not tainted 6.0.0-rc1-yoctodev-standard+
> Call Trace:
> <TASK>
> dump_stack_lvl+0x5b/0x86
> dump_stack+0x10/0x16
> check_preemption_disabled+0xe5/0xf0
> __this_cpu_preempt_check+0x13/0x20
> rcu_force_quiescent_state.part.0+0x1c/0x170
> rcu_force_quiescent_state+0x1e/0x30
> rcu_torture_fqs+0xca/0x160
> ? rcu_torture_boost+0x430/0x430
> kthread+0x192/0x1d0
> ? kthread_complete_and_exit+0x30/0x30
> ret_from_fork+0x22/0x30
> </TASK>
>
> When enable rcutorture.fqs_duration, the rcu_force_quiescent_state() be
> invoked in rcu_torture_fqs task context, invoke __this_cpu_read() in
> preemptible code section will trigger the above calltrace.
Makes sense, so in theory the GP thread might get migrated after sampling
rcu_data.mynode but that's Ok since it wont change the behavior of the code
following it AFAICS.
Reviewed-by: Joel Fernandes (Google) <joel@joelfernandes.org>
thanks,
- Joel
> This commit convert __this_cpu_read() to raw_cpu_read() to avoid
> this warning.
>
> Signed-off-by: Zqiang <qiang1.zhang@intel.com>
> ---
> kernel/rcu/tree.c | 2 +-
> 1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> index 96d678c9cfb6..282002e62cf3 100644
> --- a/kernel/rcu/tree.c
> +++ b/kernel/rcu/tree.c
> @@ -2436,7 +2436,7 @@ void rcu_force_quiescent_state(void)
> struct rcu_node *rnp_old = NULL;
>
> /* Funnel through hierarchy to reduce memory contention. */
> - rnp = __this_cpu_read(rcu_data.mynode);
> + rnp = raw_cpu_read(rcu_data.mynode);
> for (; rnp != NULL; rnp = rnp->parent) {
> ret = (READ_ONCE(rcu_state.gp_flags) & RCU_GP_FLAG_FQS) ||
> !raw_spin_trylock(&rnp->fqslock);
> --
> 2.25.1
>
next prev parent reply other threads:[~2022-10-13 15:40 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-10-13 4:41 [PATCH] rcu: Fix use __this_cpu_read() warning in preemptible code Zqiang
2022-10-13 14:13 ` Paul E. McKenney
2022-10-13 15:39 ` Joel Fernandes [this message]
2022-10-14 14:38 ` Paul E. McKenney
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