Messages in this thread | | | Date | Wed, 9 Mar 2022 11:08:39 +0800 | Subject | Re: [External] Re: [PATCH v3 2/3] sched/cpuacct: optimize away RCU read lock | From | Chengming Zhou <> |
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On 2022/3/9 7:20 上午, Marek Szyprowski wrote: > On 20.02.2022 06:14, Chengming Zhou wrote: >> Since cpuacct_charge() is called from the scheduler update_curr(), >> we must already have rq lock held, then the RCU read lock can >> be optimized away. >> >> And do the same thing in it's wrapper cgroup_account_cputime(), >> but we can't use lockdep_assert_rq_held() there, which defined >> in kernel/sched/sched.h. >> >> Suggested-by: Peter Zijlstra (Intel) <peterz@infradead.org> >> Signed-off-by: Chengming Zhou <zhouchengming@bytedance.com> > > This patch landed recently in linux-next as commit dc6e0818bc9a > ("sched/cpuacct: Optimize away RCU read lock"). On my test systems I > found that it triggers a following warning in the early boot stage:
Hi, thanks for the report. I've send a fix patch[1] for review.
[1] https://lore.kernel.org/lkml/20220305034103.57123-1-zhouchengming@bytedance.com/
> > Calibrating delay loop (skipped), value calculated using timer > frequency.. 48.00 BogoMIPS (lpj=240000) > pid_max: default: 32768 minimum: 301 > Mount-cache hash table entries: 2048 (order: 1, 8192 bytes, linear) > Mountpoint-cache hash table entries: 2048 (order: 1, 8192 bytes, linear) > CPU: Testing write buffer coherency: ok > CPU0: Spectre v2: using BPIALL workaround > > ============================= > WARNING: suspicious RCU usage > 5.17.0-rc5-00050-gdc6e0818bc9a #11458 Not tainted > ----------------------------- > ./include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 1 > 2 locks held by kthreadd/2: > #0: c1d7972c (&p->pi_lock){....}-{2:2}, at: task_rq_lock+0x30/0x118 > #1: ef7b52d0 (&rq->__lock){-...}-{2:2}, at: > raw_spin_rq_lock_nested+0x24/0x34 > > stack backtrace: > CPU: 0 PID: 2 Comm: kthreadd Not tainted 5.17.0-rc5-00050-gdc6e0818bc9a > #11458 > Hardware name: Samsung Exynos (Flattened Device Tree) > unwind_backtrace from show_stack+0x10/0x14 > show_stack from dump_stack_lvl+0x58/0x70 > dump_stack_lvl from update_curr+0x1bc/0x35c > update_curr from dequeue_task_fair+0xb0/0x8e8 > dequeue_task_fair from __do_set_cpus_allowed+0x19c/0x258 > __do_set_cpus_allowed from __set_cpus_allowed_ptr_locked+0x130/0x1d8 > __set_cpus_allowed_ptr_locked from __set_cpus_allowed_ptr+0x48/0x64 > __set_cpus_allowed_ptr from kthreadd+0x44/0x16c > kthreadd from ret_from_fork+0x14/0x2c > Exception stack(0xc1cb9fb0 to 0xc1cb9ff8) > 9fa0: 00000000 00000000 00000000 > 00000000 > 9fc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 > 00000000 > 9fe0: 00000000 00000000 00000000 00000000 00000013 00000000 > CPU0: thread -1, cpu 0, socket 9, mpidr 80000900 > cblist_init_generic: Setting adjustable number of callback queues. > cblist_init_generic: Setting shift to 1 and lim to 1. > Running RCU-tasks wait API self tests > Setting up static identity map for 0x40100000 - 0x40100060 > rcu: Hierarchical SRCU implementation. > > ============================= > WARNING: suspicious RCU usage > 5.17.0-rc5-00050-gdc6e0818bc9a #11458 Not tainted > ----------------------------- > ./include/linux/cgroup.h:481 suspicious rcu_dereference_check() usage! > > other info that might help us debug this: > > > rcu_scheduler_active = 1, debug_locks = 1 > 1 lock held by migration/0/13: > #0: ef7b52d0 (&rq->__lock){-...}-{2:2}, at: > raw_spin_rq_lock_nested+0x24/0x34 > > stack backtrace: > CPU: 0 PID: 13 Comm: migration/0 Not tainted > 5.17.0-rc5-00050-gdc6e0818bc9a #11458 > Hardware name: Samsung Exynos (Flattened Device Tree) > Stopper: 0x0 <- 0x0 > unwind_backtrace from show_stack+0x10/0x14 > show_stack from dump_stack_lvl+0x58/0x70 > dump_stack_lvl from put_prev_task_stop+0x16c/0x25c > put_prev_task_stop from __schedule+0x698/0x964 > __schedule from schedule+0x54/0xe0 > schedule from smpboot_thread_fn+0x218/0x288 > smpboot_thread_fn from kthread+0xf0/0x134 > kthread from ret_from_fork+0x14/0x2c > Exception stack(0xc1ccffb0 to 0xc1ccfff8) > ffa0: 00000000 00000000 00000000 > 00000000 > ffc0: 00000000 00000000 00000000 00000000 00000000 00000000 00000000 > 00000000 > ffe0: 00000000 00000000 00000000 00000000 00000013 00000000 > smp: Bringing up secondary CPUs ... > CPU1: thread -1, cpu 1, socket 9, mpidr 80000901 > CPU1: Spectre v2: using BPIALL workaround > smp: Brought up 1 node, 2 CPUs > SMP: Total of 2 processors activated (96.00 BogoMIPS). > > The above log comes from ARM 32bit Samsung Exnyos4210 based Trats board. > >> --- >> include/linux/cgroup.h | 2 -- >> kernel/sched/cpuacct.c | 4 +--- >> 2 files changed, 1 insertion(+), 5 deletions(-) >> >> diff --git a/include/linux/cgroup.h b/include/linux/cgroup.h >> index 75c151413fda..9a109c6ac0e0 100644 >> --- a/include/linux/cgroup.h >> +++ b/include/linux/cgroup.h >> @@ -791,11 +791,9 @@ static inline void cgroup_account_cputime(struct task_struct *task, >> >> cpuacct_charge(task, delta_exec); >> >> - rcu_read_lock(); >> cgrp = task_dfl_cgroup(task); >> if (cgroup_parent(cgrp)) >> __cgroup_account_cputime(cgrp, delta_exec); >> - rcu_read_unlock(); >> } >> >> static inline void cgroup_account_cputime_field(struct task_struct *task, >> diff --git a/kernel/sched/cpuacct.c b/kernel/sched/cpuacct.c >> index 307800586ac8..f79f88456d72 100644 >> --- a/kernel/sched/cpuacct.c >> +++ b/kernel/sched/cpuacct.c >> @@ -337,12 +337,10 @@ void cpuacct_charge(struct task_struct *tsk, u64 cputime) >> unsigned int cpu = task_cpu(tsk); >> struct cpuacct *ca; >> >> - rcu_read_lock(); >> + lockdep_assert_rq_held(cpu_rq(cpu)); >> >> for (ca = task_ca(tsk); ca; ca = parent_ca(ca)) >> *per_cpu_ptr(ca->cpuusage, cpu) += cputime; >> - >> - rcu_read_unlock(); >> } >> >> /* > > Best regards
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