Messages in this thread Patch in this message | | | Date | Thu, 27 Feb 2020 11:41:37 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing |
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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)); >
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