2022-05-23 07:00:35

by Zqiang

Subject: [PATCH] rcu/rcuscale: Fix using smp_processor_id() in preemptible warnings

BUG: using smp_processor_id() in preemptible [00000000] code: rcu_scale_write/69
CPU: 0 PID: 66 Comm: rcu_scale_write Not tainted 5.18.0-rc7-next-20220517-yoctodev-standard+
caller is debug_smp_processor_id+0x17/0x20
Call Trace:
<TASK>
dump_stack_lvl+0x49/0x5e
dump_stack+0x10/0x12
check_preemption_disabled+0xdf/0xf0
debug_smp_processor_id+0x17/0x20
rcu_scale_writer+0x2b5/0x580
kthread+0x177/0x1b0
ret_from_fork+0x22/0x30
</TASK>

Reproduction method:
runqemu kvm slirp nographic qemuparams="-m 4096 -smp 8" bootparams="isolcpus=2,3
nohz_full=2,3 rcu_nocbs=2,3 rcutree.dump_tree=1 rcuscale.shutdown=false
rcuscale.gp_async=true" -d

when the CONFIG_DEBUG_PREEMPT is enabled, this_cpu_ptr() will call
debug_smp_processor_id() get current CPU number, this warning is triggered by
is_percpu_thread() in debug_smp_processor_id(), the is_percpu_thread() need to
check whether 'current->nr_cpus_allowed == 1' and 'current->flags & PF_NO_SETAFFINITY',
invoke set_cpus_allowed_ptr() only set kthreads->nr_cpus_allowed, but the
PF_NO_SETAFFINITY is not set to kthread->flags, so add PF_NO_SETAFFINITY flags
setting.

Signed-off-by: Zqiang <[email protected]>
---
kernel/rcu/rcuscale.c | 1 +
1 file changed, 1 insertion(+)

diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
index 277a5bfb37d4..3ef02d4a8108 100644
--- a/kernel/rcu/rcuscale.c
+++ b/kernel/rcu/rcuscale.c
@@ -419,6 +419,7 @@ rcu_scale_writer(void *arg)
VERBOSE_SCALEOUT_STRING("rcu_scale_writer task started");
WARN_ON(!wdpp);
set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
+ current->flags |= PF_NO_SETAFFINITY;
sched_set_fifo_low(current);

if (holdoff)
--
2.25.1

2022-05-24 06:28:13

by Paul E. McKenney

Subject: Re: [PATCH] rcu/rcuscale: Fix using smp_processor_id() in preemptible warnings

On Sat, May 21, 2022 at 02:56:26PM +0800, Zqiang wrote:
> BUG: using smp_processor_id() in preemptible [00000000] code: rcu_scale_write/69
> CPU: 0 PID: 66 Comm: rcu_scale_write Not tainted 5.18.0-rc7-next-20220517-yoctodev-standard+
> caller is debug_smp_processor_id+0x17/0x20
> Call Trace:
> <TASK>
> dump_stack_lvl+0x49/0x5e
> dump_stack+0x10/0x12
> check_preemption_disabled+0xdf/0xf0
> debug_smp_processor_id+0x17/0x20
> rcu_scale_writer+0x2b5/0x580
> kthread+0x177/0x1b0
> ret_from_fork+0x22/0x30
> </TASK>
>
> Reproduction method:
> runqemu kvm slirp nographic qemuparams="-m 4096 -smp 8" bootparams="isolcpus=2,3
> nohz_full=2,3 rcu_nocbs=2,3 rcutree.dump_tree=1 rcuscale.shutdown=false
> rcuscale.gp_async=true" -d
>
> when the CONFIG_DEBUG_PREEMPT is enabled, this_cpu_ptr() will call
> debug_smp_processor_id() get current CPU number, this warning is triggered by
> is_percpu_thread() in debug_smp_processor_id(), the is_percpu_thread() need to
> check whether 'current->nr_cpus_allowed == 1' and 'current->flags & PF_NO_SETAFFINITY',
> invoke set_cpus_allowed_ptr() only set kthreads->nr_cpus_allowed, but the
> PF_NO_SETAFFINITY is not set to kthread->flags, so add PF_NO_SETAFFINITY flags
> setting.
>
> Signed-off-by: Zqiang <[email protected]>

Good catch! Queued for v5.20 (or v6.0, as Linus decides), thank you!

Thanx, Paul

> ---
> kernel/rcu/rcuscale.c | 1 +
> 1 file changed, 1 insertion(+)
>
> diff --git a/kernel/rcu/rcuscale.c b/kernel/rcu/rcuscale.c
> index 277a5bfb37d4..3ef02d4a8108 100644
> --- a/kernel/rcu/rcuscale.c
> +++ b/kernel/rcu/rcuscale.c
> @@ -419,6 +419,7 @@ rcu_scale_writer(void *arg)
> VERBOSE_SCALEOUT_STRING("rcu_scale_writer task started");
> WARN_ON(!wdpp);
> set_cpus_allowed_ptr(current, cpumask_of(me % nr_cpu_ids));
> + current->flags |= PF_NO_SETAFFINITY;
> sched_set_fifo_low(current);
>
> if (holdoff)
> --
> 2.25.1
>