Messages in this thread Patch in this message | | | Date | Fri, 06 Mar 2020 14:42:07 -0000 | From | "tip-bot2 for Mel Gorman" <> | Subject | [tip: sched/core] sched/numa: Acquire RCU lock for checking idle cores during NUMA balancing |
| |
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));
| |