* [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing
@ 2020-02-27 19:18 Mel Gorman
2020-02-27 19:41 ` Paul E. McKenney
2020-03-06 14:42 ` [tip: sched/core] " tip-bot2 for Mel Gorman
0 siblings, 2 replies; 3+ messages in thread
From: Mel Gorman @ 2020-02-27 19:18 UTC (permalink / raw)
To: Ingo Molnar
Cc: Qian Cai, Peter Zijlstra, Juri Lelli, Steven Rostedt,
Valentin Schneider, paulmck, linux-kernel
Qian Cai reported the following
The linux-next commit ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a
migration target instead of comparing tasks") introduced a boot warning,
[ 86.520534][ T1] WARNING: suspicious RCU usage
[ 86.520540][ T1] 5.6.0-rc3-next-20200227 #7 Not tainted
[ 86.520545][ T1] -----------------------------
[ 86.520551][ T1] kernel/sched/fair.c:5914 suspicious rcu_dereference_check() usage!
[ 86.520555][ T1]
[ 86.520555][ T1] other info that might help us debug this:
[ 86.520555][ T1]
[ 86.520561][ T1]
[ 86.520561][ T1] rcu_scheduler_active = 2, debug_locks = 1
[ 86.520567][ T1] 1 lock held by systemd/1:
[ 86.520571][ T1] #0: ffff8887f4b14848 (&mm->mmap_sem#2){++++}, at: do_page_fault+0x1d2/0x998
[ 86.520594][ T1]
[ 86.520594][ T1] stack backtrace:
[ 86.520602][ T1] CPU: 1 PID: 1 Comm: systemd Not tainted 5.6.0-rc3-next-20200227 #7
task_numa_migrate() checks for idle cores when updating NUMA-related statistics.
This relies on reading a RCU-protected structure in test_idle_cores() via this
call chain
task_numa_migrate
-> update_numa_stats
-> numa_idle_core
-> test_idle_cores
While the locking could be fine-grained, it is more appropriate to acquire
the RCU lock for the entire scan of the domain. This patch removes the
warning triggered at boot time.
Fixes: ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a migration target instead of comparing tasks")
Reported-by: Qian Cai <cai@lca.pw>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
---
kernel/sched/fair.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 10f9e6729fcf..1592b6d26239 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1595,6 +1595,7 @@ static void update_numa_stats(struct task_numa_env *env,
memset(ns, 0, sizeof(*ns));
ns->idle_cpu = -1;
+ rcu_read_lock();
for_each_cpu(cpu, cpumask_of_node(nid)) {
struct rq *rq = cpu_rq(cpu);
@@ -1614,6 +1615,7 @@ static void update_numa_stats(struct task_numa_env *env,
idle_core = numa_idle_core(idle_core, cpu);
}
}
+ rcu_read_unlock();
ns->weight = cpumask_weight(cpumask_of_node(nid));
^ permalink raw reply related [flat|nested] 3+ messages in thread* Re: [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing
2020-02-27 19:18 [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing Mel Gorman
@ 2020-02-27 19:41 ` Paul E. McKenney
2020-03-06 14:42 ` [tip: sched/core] " tip-bot2 for Mel Gorman
1 sibling, 0 replies; 3+ messages in thread
From: Paul E. McKenney @ 2020-02-27 19:41 UTC (permalink / raw)
To: Mel Gorman
Cc: Ingo Molnar, Qian Cai, Peter Zijlstra, Juri Lelli, Steven Rostedt,
Valentin Schneider, linux-kernel
On Thu, Feb 27, 2020 at 07:18:04PM +0000, Mel Gorman wrote:
> Qian Cai reported the following
>
> The linux-next commit ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a
> migration target instead of comparing tasks") introduced a boot warning,
>
> [ 86.520534][ T1] WARNING: suspicious RCU usage
> [ 86.520540][ T1] 5.6.0-rc3-next-20200227 #7 Not tainted
> [ 86.520545][ T1] -----------------------------
> [ 86.520551][ T1] kernel/sched/fair.c:5914 suspicious rcu_dereference_check() usage!
> [ 86.520555][ T1]
> [ 86.520555][ T1] other info that might help us debug this:
> [ 86.520555][ T1]
> [ 86.520561][ T1]
> [ 86.520561][ T1] rcu_scheduler_active = 2, debug_locks = 1
> [ 86.520567][ T1] 1 lock held by systemd/1:
> [ 86.520571][ T1] #0: ffff8887f4b14848 (&mm->mmap_sem#2){++++}, at: do_page_fault+0x1d2/0x998
> [ 86.520594][ T1]
> [ 86.520594][ T1] stack backtrace:
> [ 86.520602][ T1] CPU: 1 PID: 1 Comm: systemd Not tainted 5.6.0-rc3-next-20200227 #7
>
> task_numa_migrate() checks for idle cores when updating NUMA-related statistics.
> This relies on reading a RCU-protected structure in test_idle_cores() via this
> call chain
>
> task_numa_migrate
> -> update_numa_stats
> -> numa_idle_core
> -> test_idle_cores
>
> While the locking could be fine-grained, it is more appropriate to acquire
> the RCU lock for the entire scan of the domain. This patch removes the
> warning triggered at boot time.
>
> Fixes: ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a migration target instead of comparing tasks")
> Reported-by: Qian Cai <cai@lca.pw>
> Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
From an RCU viewpoint:
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
> ---
> kernel/sched/fair.c | 2 ++
> 1 file changed, 2 insertions(+)
>
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 10f9e6729fcf..1592b6d26239 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -1595,6 +1595,7 @@ static void update_numa_stats(struct task_numa_env *env,
> memset(ns, 0, sizeof(*ns));
> ns->idle_cpu = -1;
>
> + rcu_read_lock();
> for_each_cpu(cpu, cpumask_of_node(nid)) {
> struct rq *rq = cpu_rq(cpu);
>
> @@ -1614,6 +1615,7 @@ static void update_numa_stats(struct task_numa_env *env,
> idle_core = numa_idle_core(idle_core, cpu);
> }
> }
> + rcu_read_unlock();
>
> ns->weight = cpumask_weight(cpumask_of_node(nid));
>
^ permalink raw reply [flat|nested] 3+ messages in thread* [tip: sched/core] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing
2020-02-27 19:18 [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing Mel Gorman
2020-02-27 19:41 ` Paul E. McKenney
@ 2020-03-06 14:42 ` tip-bot2 for Mel Gorman
1 sibling, 0 replies; 3+ messages in thread
From: tip-bot2 for Mel Gorman @ 2020-03-06 14:42 UTC (permalink / raw)
To: linux-tip-commits
Cc: Qian Cai, Paul E. McKenney, Mel Gorman, Peter Zijlstra (Intel),
Ingo Molnar, x86, LKML
The following commit has been merged into the sched/core branch of tip:
Commit-ID: 0621df315402dd7bc56f7272fae9778701289825
Gitweb: https://git.kernel.org/tip/0621df315402dd7bc56f7272fae9778701289825
Author: Mel Gorman <mgorman@techsingularity.net>
AuthorDate: Thu, 27 Feb 2020 19:18:04
Committer: Ingo Molnar <mingo@kernel.org>
CommitterDate: Fri, 06 Mar 2020 12:57:22 +01:00
sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing
Qian Cai reported the following bug:
The linux-next commit ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a
migration target instead of comparing tasks") introduced a boot warning,
[ 86.520534][ T1] WARNING: suspicious RCU usage
[ 86.520540][ T1] 5.6.0-rc3-next-20200227 #7 Not tainted
[ 86.520545][ T1] -----------------------------
[ 86.520551][ T1] kernel/sched/fair.c:5914 suspicious rcu_dereference_check() usage!
[ 86.520555][ T1]
[ 86.520555][ T1] other info that might help us debug this:
[ 86.520555][ T1]
[ 86.520561][ T1]
[ 86.520561][ T1] rcu_scheduler_active = 2, debug_locks = 1
[ 86.520567][ T1] 1 lock held by systemd/1:
[ 86.520571][ T1] #0: ffff8887f4b14848 (&mm->mmap_sem#2){++++}, at: do_page_fault+0x1d2/0x998
[ 86.520594][ T1]
[ 86.520594][ T1] stack backtrace:
[ 86.520602][ T1] CPU: 1 PID: 1 Comm: systemd Not tainted 5.6.0-rc3-next-20200227 #7
task_numa_migrate() checks for idle cores when updating NUMA-related statistics.
This relies on reading a RCU-protected structure in test_idle_cores() via this
call chain
task_numa_migrate
-> update_numa_stats
-> numa_idle_core
-> test_idle_cores
While the locking could be fine-grained, it is more appropriate to acquire
the RCU lock for the entire scan of the domain. This patch removes the
warning triggered at boot time.
Reported-by: Qian Cai <cai@lca.pw>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Mel Gorman <mgorman@techsingularity.net>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Ingo Molnar <mingo@kernel.org>
Fixes: ff7db0bf24db ("sched/numa: Prefer using an idle CPU as a migration target instead of comparing tasks")
Link: https://lkml.kernel.org/r/20200227191804.GJ3818@techsingularity.net
---
kernel/sched/fair.c | 2 ++
1 file changed, 2 insertions(+)
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bba9452..3887b73 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -1608,6 +1608,7 @@ static void update_numa_stats(struct task_numa_env *env,
memset(ns, 0, sizeof(*ns));
ns->idle_cpu = -1;
+ rcu_read_lock();
for_each_cpu(cpu, cpumask_of_node(nid)) {
struct rq *rq = cpu_rq(cpu);
@@ -1627,6 +1628,7 @@ static void update_numa_stats(struct task_numa_env *env,
idle_core = numa_idle_core(idle_core, cpu);
}
}
+ rcu_read_unlock();
ns->weight = cpumask_weight(cpumask_of_node(nid));
^ permalink raw reply related [flat|nested] 3+ messages in thread
end of thread, other threads:[~2020-03-06 14:42 UTC | newest]
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2020-02-27 19:18 [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing Mel Gorman
2020-02-27 19:41 ` Paul E. McKenney
2020-03-06 14:42 ` [tip: sched/core] " tip-bot2 for Mel Gorman
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