Re: [PATCH RFC] sched: Use sched-RCU in core-scheduling balancing logic
On Thu, May 21, 2020 at 6:52 PM Paul E. McKenney wrote:
>
> On Wed, May 20, 2020 at 06:48:18PM -0400, Joel Fernandes (Google) wrote:
> > rcu_read_unlock() can incur an infrequent deadlock in
> > sched_core_balance(). Fix this by using sched-RCU instead.
> >
> > This fixes the following spinlock recursion observed when testing the
> > core scheduling patches on PREEMPT=y kernel on ChromeOS:
> >
> > [3.240891] BUG: spinlock recursion on CPU#2, swapper/2/0
> > [3.240900] lock: 0x9cd1eeb28e40, .magic: dead4ead, .owner:
> > swapper/2/0, .owner_cpu: 2
> > [3.240905] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.4.22htcore #4
> > [3.240908] Hardware name: Google Eve/Eve, BIOS Google_Eve.9584.174.0
> > 05/29/2018
> > [3.240910] Call Trace:
> > [3.240919] dump_stack+0x97/0xdb
> > [3.240924] ? spin_bug+0xa4/0xb1
> > [3.240927] do_raw_spin_lock+0x79/0x98
> > [3.240931] try_to_wake_up+0x367/0x61b
> > [3.240935] rcu_read_unlock_special+0xde/0x169
> > [3.240938] ? sched_core_balance+0xd9/0x11e
> > [3.240941] __rcu_read_unlock+0x48/0x4a
> > [3.240945] __balance_callback+0x50/0xa1
> > [3.240949] __schedule+0x55a/0x61e
> > [3.240952] schedule_idle+0x21/0x2d
> > [3.240956] do_idle+0x1d5/0x1f8
> > [3.240960] cpu_startup_entry+0x1d/0x1f
> > [3.240964] start_secondary+0x159/0x174
> > [3.240967] secondary_startup_64+0xa4/0xb0
> > [ 14.998590] watchdog: BUG: soft lockup - CPU#0 stuck for 11s!
> > [kworker/0:10:965]
> >
> > Cc: vpillai
> > Cc: Aaron Lu
> > Cc: Aubrey Li
> > Cc: pet...@infradead.org
> > Cc: paul...@kernel.org
> > Signed-off-by: Joel Fernandes (Google)
> > Change-Id: I1a4bf0cd1426b3c21ad5de44719813ad4ee5805e
>
> With some luck, the commit removing the need for this will hit
> mainline during the next merge window. Fingers firmly crossed...
Sounds good, thank you Paul :-)
- Joel
>
> Thanx, Paul
>
> > ---
> > kernel/sched/core.c | 4 ++--
> > 1 file changed, 2 insertions(+), 2 deletions(-)
> >
> > diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> > index 780514d03da47..b8ca6fcaaaf06 100644
> > --- a/kernel/sched/core.c
> > +++ b/kernel/sched/core.c
> > @@ -4897,7 +4897,7 @@ static void sched_core_balance(struct rq *rq)
> > struct sched_domain *sd;
> > int cpu = cpu_of(rq);
> >
> > - rcu_read_lock();
> > + rcu_read_lock_sched();
> > raw_spin_unlock_irq(rq_lockp(rq));
> > for_each_domain(cpu, sd) {
> > if (!(sd->flags & SD_LOAD_BALANCE))
> > @@ -4910,7 +4910,7 @@ static void sched_core_balance(struct rq *rq)
> > break;
> > }
> > raw_spin_lock_irq(rq_lockp(rq));
> > - rcu_read_unlock();
> > + rcu_read_unlock_sched();
> > }
> >
> > static DEFINE_PER_CPU(struct callback_head, core_balance_head);
> > --
> > 2.26.2.761.g0e0b3e54be-goog
> >
Re: [PATCH RFC] sched: Use sched-RCU in core-scheduling balancing logic
On Wed, May 20, 2020 at 06:48:18PM -0400, Joel Fernandes (Google) wrote:
> rcu_read_unlock() can incur an infrequent deadlock in
> sched_core_balance(). Fix this by using sched-RCU instead.
>
> This fixes the following spinlock recursion observed when testing the
> core scheduling patches on PREEMPT=y kernel on ChromeOS:
>
> [3.240891] BUG: spinlock recursion on CPU#2, swapper/2/0
> [3.240900] lock: 0x9cd1eeb28e40, .magic: dead4ead, .owner:
> swapper/2/0, .owner_cpu: 2
> [3.240905] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.4.22htcore #4
> [3.240908] Hardware name: Google Eve/Eve, BIOS Google_Eve.9584.174.0
> 05/29/2018
> [3.240910] Call Trace:
> [3.240919] dump_stack+0x97/0xdb
> [3.240924] ? spin_bug+0xa4/0xb1
> [3.240927] do_raw_spin_lock+0x79/0x98
> [3.240931] try_to_wake_up+0x367/0x61b
> [3.240935] rcu_read_unlock_special+0xde/0x169
> [3.240938] ? sched_core_balance+0xd9/0x11e
> [3.240941] __rcu_read_unlock+0x48/0x4a
> [3.240945] __balance_callback+0x50/0xa1
> [3.240949] __schedule+0x55a/0x61e
> [3.240952] schedule_idle+0x21/0x2d
> [3.240956] do_idle+0x1d5/0x1f8
> [3.240960] cpu_startup_entry+0x1d/0x1f
> [3.240964] start_secondary+0x159/0x174
> [3.240967] secondary_startup_64+0xa4/0xb0
> [ 14.998590] watchdog: BUG: soft lockup - CPU#0 stuck for 11s!
> [kworker/0:10:965]
>
> Cc: vpillai
> Cc: Aaron Lu
> Cc: Aubrey Li
> Cc: pet...@infradead.org
> Cc: paul...@kernel.org
> Signed-off-by: Joel Fernandes (Google)
> Change-Id: I1a4bf0cd1426b3c21ad5de44719813ad4ee5805e
With some luck, the commit removing the need for this will hit
mainline during the next merge window. Fingers firmly crossed...
Thanx, Paul
> ---
> kernel/sched/core.c | 4 ++--
> 1 file changed, 2 insertions(+), 2 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 780514d03da47..b8ca6fcaaaf06 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4897,7 +4897,7 @@ static void sched_core_balance(struct rq *rq)
> struct sched_domain *sd;
> int cpu = cpu_of(rq);
>
> - rcu_read_lock();
> + rcu_read_lock_sched();
> raw_spin_unlock_irq(rq_lockp(rq));
> for_each_domain(cpu, sd) {
> if (!(sd->flags & SD_LOAD_BALANCE))
> @@ -4910,7 +4910,7 @@ static void sched_core_balance(struct rq *rq)
> break;
> }
> raw_spin_lock_irq(rq_lockp(rq));
> - rcu_read_unlock();
> + rcu_read_unlock_sched();
> }
>
> static DEFINE_PER_CPU(struct callback_head, core_balance_head);
> --
> 2.26.2.761.g0e0b3e54be-goog
>
[PATCH RFC] sched: Use sched-RCU in core-scheduling balancing logic
rcu_read_unlock() can incur an infrequent deadlock in
sched_core_balance(). Fix this by using sched-RCU instead.
This fixes the following spinlock recursion observed when testing the
core scheduling patches on PREEMPT=y kernel on ChromeOS:
[3.240891] BUG: spinlock recursion on CPU#2, swapper/2/0
[3.240900] lock: 0x9cd1eeb28e40, .magic: dead4ead, .owner:
swapper/2/0, .owner_cpu: 2
[3.240905] CPU: 2 PID: 0 Comm: swapper/2 Not tainted 5.4.22htcore #4
[3.240908] Hardware name: Google Eve/Eve, BIOS Google_Eve.9584.174.0
05/29/2018
[3.240910] Call Trace:
[3.240919] dump_stack+0x97/0xdb
[3.240924] ? spin_bug+0xa4/0xb1
[3.240927] do_raw_spin_lock+0x79/0x98
[3.240931] try_to_wake_up+0x367/0x61b
[3.240935] rcu_read_unlock_special+0xde/0x169
[3.240938] ? sched_core_balance+0xd9/0x11e
[3.240941] __rcu_read_unlock+0x48/0x4a
[3.240945] __balance_callback+0x50/0xa1
[3.240949] __schedule+0x55a/0x61e
[3.240952] schedule_idle+0x21/0x2d
[3.240956] do_idle+0x1d5/0x1f8
[3.240960] cpu_startup_entry+0x1d/0x1f
[3.240964] start_secondary+0x159/0x174
[3.240967] secondary_startup_64+0xa4/0xb0
[ 14.998590] watchdog: BUG: soft lockup - CPU#0 stuck for 11s!
[kworker/0:10:965]
Cc: vpillai
Cc: Aaron Lu
Cc: Aubrey Li
Cc: pet...@infradead.org
Cc: paul...@kernel.org
Signed-off-by: Joel Fernandes (Google)
Change-Id: I1a4bf0cd1426b3c21ad5de44719813ad4ee5805e
---
kernel/sched/core.c | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)
diff --git a/kernel/sched/core.c b/kernel/sched/core.c
index 780514d03da47..b8ca6fcaaaf06 100644
--- a/kernel/sched/core.c
+++ b/kernel/sched/core.c
@@ -4897,7 +4897,7 @@ static void sched_core_balance(struct rq *rq)
struct sched_domain *sd;
int cpu = cpu_of(rq);
- rcu_read_lock();
+ rcu_read_lock_sched();
raw_spin_unlock_irq(rq_lockp(rq));
for_each_domain(cpu, sd) {
if (!(sd->flags & SD_LOAD_BALANCE))
@@ -4910,7 +4910,7 @@ static void sched_core_balance(struct rq *rq)
break;
}
raw_spin_lock_irq(rq_lockp(rq));
- rcu_read_unlock();
+ rcu_read_unlock_sched();
}
static DEFINE_PER_CPU(struct callback_head, core_balance_head);
--
2.26.2.761.g0e0b3e54be-goog
