From: Mel Gorman <mgorman@techsingularity.net>
To: Ingo Molnar <mingo@kernel.org>
Cc: Qian Cai <cai@lca.pw>, Peter Zijlstra <a.p.zijlstra@chello.nl>,
Juri Lelli <juri.lelli@redhat.com>,
Steven Rostedt <rostedt@goodmis.org>,
Valentin Schneider <valentin.schneider@arm.com>,
paulmck@kernel.org, linux-kernel@vger.kernel.org
Subject: [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing
Date: Thu, 27 Feb 2020 19:18:04 +0000 [thread overview]
Message-ID: <20200227191804.GJ3818@techsingularity.net> (raw)
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));
next reply other threads:[~2020-02-27 19:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-27 19:18 Mel Gorman [this message]
2020-02-27 19:41 ` [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing Paul E. McKenney
2020-03-06 14:42 ` [tip: sched/core] " tip-bot2 for Mel Gorman
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20200227191804.GJ3818@techsingularity.net \
--to=mgorman@techsingularity.net \
--cc=a.p.zijlstra@chello.nl \
--cc=cai@lca.pw \
--cc=juri.lelli@redhat.com \
--cc=linux-kernel@vger.kernel.org \
--cc=mingo@kernel.org \
--cc=paulmck@kernel.org \
--cc=rostedt@goodmis.org \
--cc=valentin.schneider@arm.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).