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authorMel Gorman <mgorman@techsingularity.net>2020-02-27 19:18:04 +0000
committerIngo Molnar <mingo@kernel.org>2020-03-06 12:57:22 +0100
commit0621df315402dd7bc56f7272fae9778701289825 (patch)
treeec89f2564e649065d675cb2353e9fa8c9e1cc405 /kernel/sched/fair.c
parent76c389ab2b5e300698eab87f9d4b7916f14117ba (diff)
downloadlinux-0621df315402dd7bc56f7272fae9778701289825.tar.gz
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
Diffstat (limited to 'kernel/sched/fair.c')
-rw-r--r--kernel/sched/fair.c2
1 files changed, 2 insertions, 0 deletions
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index bba945277205..3887b7323abd 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));