After commit 8ad075c2eb1f ("sched: Async unthrottling for cfs
bandwidth"), we may update the rq clock multiple times in the loop of
__cfsb_csd_unthrottle(). At that time the following warning will be
triggered.
------------[ cut here ]------------
rq->clock_update_flags & RQCF_UPDATED
WARNING: CPU: 54 PID: 0 at kernel/sched/core.c:741
update_rq_clock+0xaf/0x180
Call Trace:
<TASK>
unthrottle_cfs_rq+0x4b/0x300
__cfsb_csd_unthrottle+0xe0/0x100
__flush_smp_call_function_queue+0xaf/0x1d0
flush_smp_call_function_queue+0x49/0x90
do_idle+0x17c/0x270
cpu_startup_entry+0x19/0x20
start_secondary+0xfa/0x120
secondary_startup_64_no_verify+0xce/0xdb
Before the loop starts, we update the rq clock once and call
rq_clock_start_loop_update() to prevent updating the rq clock
multiple times. And call rq_clock_stop_loop_update() After
the loop to clear rq->clock_update_flags.
Fixes: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
Suggested-by: Vincent Guittot <[email protected]>
Signed-off-by: Hao Jia <[email protected]>
---
kernel/sched/fair.c | 9 +++++++++
kernel/sched/sched.h | 21 +++++++++++++++++++++
2 files changed, 30 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 373ff5f55884..af9604f4b135 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -5576,6 +5576,14 @@ static void __cfsb_csd_unthrottle(void *arg)
rq_lock(rq, &rf);
+ /*
+ * Iterating over the list can trigger several call to
+ * update_rq_clock() in unthrottle_cfs_rq().
+ * Do it once and skip the potential next ones.
+ */
+ update_rq_clock(rq);
+ rq_clock_start_loop_update(rq);
+
/*
* Since we hold rq lock we're safe from concurrent manipulation of
* the CSD list. However, this RCU critical section annotates the
@@ -5595,6 +5603,7 @@ static void __cfsb_csd_unthrottle(void *arg)
rcu_read_unlock();
+ rq_clock_stop_loop_update(rq);
rq_unlock(rq, &rf);
}
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index ec7b3e0a2b20..50446e401b9f 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1546,6 +1546,27 @@ static inline void rq_clock_cancel_skipupdate(struct rq *rq)
rq->clock_update_flags &= ~RQCF_REQ_SKIP;
}
+/*
+ * During cpu offlining and rq wide unthrottling, we can trigger
+ * an update_rq_clock() for several cfs and rt runqueues (Typically
+ * when using list_for_each_entry_*)
+ * rq_clock_start_loop_update() can be called after updating the clock
+ * once and before iterating over the list to prevent multiple update.
+ * After the iterative traversal, we need to call rq_clock_stop_loop_update()
+ * to clear RQCF_ACT_SKIP of rq->clock_update_flags.
+ */
+static inline void rq_clock_start_loop_update(struct rq *rq)
+{
+ lockdep_assert_rq_held(rq);
+ rq->clock_update_flags |= RQCF_ACT_SKIP;
+}
+
+static inline void rq_clock_stop_loop_update(struct rq *rq)
+{
+ lockdep_assert_rq_held(rq);
+ rq->clock_update_flags &= ~RQCF_ACT_SKIP;
+}
+
struct rq_flags {
unsigned long flags;
struct pin_cookie cookie;
--
2.37.0
On Mon, 15 May 2023 at 08:39, Hao Jia <[email protected]> wrote:
>
> After commit 8ad075c2eb1f ("sched: Async unthrottling for cfs
> bandwidth"), we may update the rq clock multiple times in the loop of
> __cfsb_csd_unthrottle(). At that time the following warning will be
> triggered.
> ------------[ cut here ]------------
> rq->clock_update_flags & RQCF_UPDATED
> WARNING: CPU: 54 PID: 0 at kernel/sched/core.c:741
> update_rq_clock+0xaf/0x180
> Call Trace:
> <TASK>
> unthrottle_cfs_rq+0x4b/0x300
> __cfsb_csd_unthrottle+0xe0/0x100
> __flush_smp_call_function_queue+0xaf/0x1d0
> flush_smp_call_function_queue+0x49/0x90
> do_idle+0x17c/0x270
> cpu_startup_entry+0x19/0x20
> start_secondary+0xfa/0x120
> secondary_startup_64_no_verify+0xce/0xdb
>
> Before the loop starts, we update the rq clock once and call
> rq_clock_start_loop_update() to prevent updating the rq clock
> multiple times. And call rq_clock_stop_loop_update() After
> the loop to clear rq->clock_update_flags.
>
> Fixes: 8ad075c2eb1f ("sched: Async unthrottling for cfs bandwidth")
>
> Suggested-by: Vincent Guittot <[email protected]>
> Signed-off-by: Hao Jia <[email protected]>
Reviewed-by: Vincent Guittot <[email protected]>
> ---
> kernel/sched/fair.c | 9 +++++++++
> kernel/sched/sched.h | 21 +++++++++++++++++++++
> 2 files changed, 30 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 373ff5f55884..af9604f4b135 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -5576,6 +5576,14 @@ static void __cfsb_csd_unthrottle(void *arg)
>
> rq_lock(rq, &rf);
>
> + /*
> + * Iterating over the list can trigger several call to
> + * update_rq_clock() in unthrottle_cfs_rq().
> + * Do it once and skip the potential next ones.
> + */
> + update_rq_clock(rq);
> + rq_clock_start_loop_update(rq);
> +
> /*
> * Since we hold rq lock we're safe from concurrent manipulation of
> * the CSD list. However, this RCU critical section annotates the
> @@ -5595,6 +5603,7 @@ static void __cfsb_csd_unthrottle(void *arg)
>
> rcu_read_unlock();
>
> + rq_clock_stop_loop_update(rq);
> rq_unlock(rq, &rf);
> }
>
> diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
> index ec7b3e0a2b20..50446e401b9f 100644
> --- a/kernel/sched/sched.h
> +++ b/kernel/sched/sched.h
> @@ -1546,6 +1546,27 @@ static inline void rq_clock_cancel_skipupdate(struct rq *rq)
> rq->clock_update_flags &= ~RQCF_REQ_SKIP;
> }
>
> +/*
> + * During cpu offlining and rq wide unthrottling, we can trigger
> + * an update_rq_clock() for several cfs and rt runqueues (Typically
> + * when using list_for_each_entry_*)
> + * rq_clock_start_loop_update() can be called after updating the clock
> + * once and before iterating over the list to prevent multiple update.
> + * After the iterative traversal, we need to call rq_clock_stop_loop_update()
> + * to clear RQCF_ACT_SKIP of rq->clock_update_flags.
> + */
> +static inline void rq_clock_start_loop_update(struct rq *rq)
> +{
> + lockdep_assert_rq_held(rq);
> + rq->clock_update_flags |= RQCF_ACT_SKIP;
> +}
> +
> +static inline void rq_clock_stop_loop_update(struct rq *rq)
> +{
> + lockdep_assert_rq_held(rq);
> + rq->clock_update_flags &= ~RQCF_ACT_SKIP;
> +}
> +
> struct rq_flags {
> unsigned long flags;
> struct pin_cookie cookie;
> --
> 2.37.0
>