| Message ID | 20230705073020.2030-2-thunder.leizhen@huawei.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | rcu: Don't dump the stalled CPU on where RCU GP kthread last ran twice | expand |
On Wed, Jul 05, 2023 at 03:30:19PM +0800, Zhen Lei wrote: > The above condition "if (gpk)" already ensures that gp_kthread is created, > so the local variable 'cpu' cannot be negative here. > > Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> > --- > kernel/rcu/tree_stall.h | 12 +++++------- > 1 file changed, 5 insertions(+), 7 deletions(-) > > diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h > index b10b8349bb2a48b..dcfaa3d5db2cbc7 100644 > --- a/kernel/rcu/tree_stall.h > +++ b/kernel/rcu/tree_stall.h > @@ -537,13 +537,11 @@ static void rcu_check_gp_kthread_starvation(void) > pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); > pr_err("RCU grace-period kthread stack dump:\n"); > sched_show_task(gpk); > - if (cpu >= 0) { I am not quite this trusting of the relation between the relationship between the existence of the grace-period khread and its CPU number being in range. Let's please start with something like this: if (!WARN_ON_ONCE(cpu < 0)) { Please note that this is not just me. See for example the use of the cpumask_check() function, albeit the opposite concern. > - if (cpu_is_offline(cpu)) { > - pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); > - } else { > - pr_err("Stack dump where RCU GP kthread last ran:\n"); > - dump_cpu_task(cpu); > - } > + if (cpu_is_offline(cpu)) { > + pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); > + } else { > + pr_err("Stack dump where RCU GP kthread last ran:\n"); > + dump_cpu_task(cpu); > } > wake_up_process(gpk); > } > -- > 2.25.1 >
On 2023/7/11 3:03, Paul E. McKenney wrote: > On Wed, Jul 05, 2023 at 03:30:19PM +0800, Zhen Lei wrote: >> The above condition "if (gpk)" already ensures that gp_kthread is created, >> so the local variable 'cpu' cannot be negative here. >> >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >> --- >> kernel/rcu/tree_stall.h | 12 +++++------- >> 1 file changed, 5 insertions(+), 7 deletions(-) >> >> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h >> index b10b8349bb2a48b..dcfaa3d5db2cbc7 100644 >> --- a/kernel/rcu/tree_stall.h >> +++ b/kernel/rcu/tree_stall.h >> @@ -537,13 +537,11 @@ static void rcu_check_gp_kthread_starvation(void) >> pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); >> pr_err("RCU grace-period kthread stack dump:\n"); >> sched_show_task(gpk); >> - if (cpu >= 0) { > > I am not quite this trusting of the relation between the relationship > between the existence of the grace-period khread and its CPU number > being in range. Let's please start with something like this: > > if (!WARN_ON_ONCE(cpu < 0)) { > > Please note that this is not just me. See for example the use of the > cpumask_check() function, albeit the opposite concern. git grep -wn "\->cpu" kernel/ include/ kernel/kthread.c:583: to_kthread(p)->cpu = cpu; //kthread_create_on_cpu() kernel/sched/sched.h:2024: WRITE_ONCE(task_thread_info(p)->cpu, cpu); //__set_task_cpu() include/linux/sched.h:2250: return READ_ONCE(task_thread_info(p)->cpu); //task_cpu() git grep -wn "\.cpu" kernel/ include/ //There is no task related, the search result is omitted. Therefore, there is only one path "set_task_cpu()-->__set_task_cpu()" that can dynamically change the value of task_cpu(p). In fact, this guarantee has been made in set_task_cpu(). set_task_cpu WARN_ON_ONCE(!cpu_online(new_cpu)); __set_task_cpu(p, new_cpu); In addition, task_struct has member 'on_rq'. Therefore, when a task leaves the scheduling queue, setting the member 'cpu' to an invalid value will be thankless. Sorry, these two patches was posted too quickly, and I'm still regretting that I should have attached this to the commit description these days. > >> - if (cpu_is_offline(cpu)) { >> - pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); >> - } else { >> - pr_err("Stack dump where RCU GP kthread last ran:\n"); >> - dump_cpu_task(cpu); >> - } >> + if (cpu_is_offline(cpu)) { >> + pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); >> + } else { >> + pr_err("Stack dump where RCU GP kthread last ran:\n"); >> + dump_cpu_task(cpu); >> } >> wake_up_process(gpk); >> } >> -- >> 2.25.1 >> > . >
On Tue, Jul 11, 2023 at 11:20:07AM +0800, Leizhen (ThunderTown) wrote: > > > On 2023/7/11 3:03, Paul E. McKenney wrote: > > On Wed, Jul 05, 2023 at 03:30:19PM +0800, Zhen Lei wrote: > >> The above condition "if (gpk)" already ensures that gp_kthread is created, > >> so the local variable 'cpu' cannot be negative here. > >> > >> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> > >> --- > >> kernel/rcu/tree_stall.h | 12 +++++------- > >> 1 file changed, 5 insertions(+), 7 deletions(-) > >> > >> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h > >> index b10b8349bb2a48b..dcfaa3d5db2cbc7 100644 > >> --- a/kernel/rcu/tree_stall.h > >> +++ b/kernel/rcu/tree_stall.h > >> @@ -537,13 +537,11 @@ static void rcu_check_gp_kthread_starvation(void) > >> pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); > >> pr_err("RCU grace-period kthread stack dump:\n"); > >> sched_show_task(gpk); > >> - if (cpu >= 0) { > > > > I am not quite this trusting of the relation between the relationship > > between the existence of the grace-period khread and its CPU number > > being in range. Let's please start with something like this: > > > > if (!WARN_ON_ONCE(cpu < 0)) { > > > > Please note that this is not just me. See for example the use of the > > cpumask_check() function, albeit the opposite concern. > > git grep -wn "\->cpu" kernel/ include/ > kernel/kthread.c:583: to_kthread(p)->cpu = cpu; //kthread_create_on_cpu() > kernel/sched/sched.h:2024: WRITE_ONCE(task_thread_info(p)->cpu, cpu); //__set_task_cpu() > include/linux/sched.h:2250: return READ_ONCE(task_thread_info(p)->cpu); //task_cpu() > > git grep -wn "\.cpu" kernel/ include/ //There is no task related, the search result is omitted. > > Therefore, there is only one path "set_task_cpu()-->__set_task_cpu()" that can dynamically > change the value of task_cpu(p). In fact, this guarantee has been made in set_task_cpu(). > set_task_cpu > WARN_ON_ONCE(!cpu_online(new_cpu)); > __set_task_cpu(p, new_cpu); > > In addition, task_struct has member 'on_rq'. Therefore, when a task leaves the scheduling > queue, setting the member 'cpu' to an invalid value will be thankless. Thank you for digging into this! Given that, as you say, we can dispense with the check. > Sorry, these two patches was posted too quickly, and I'm still regretting that I should have > attached this to the commit description these days. Please do resend the patches with this explanation in the commit log. And please don't worry about making the English pretty, as I can always wordsmith. Thanx, Paul > >> - if (cpu_is_offline(cpu)) { > >> - pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); > >> - } else { > >> - pr_err("Stack dump where RCU GP kthread last ran:\n"); > >> - dump_cpu_task(cpu); > >> - } > >> + if (cpu_is_offline(cpu)) { > >> + pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); > >> + } else { > >> + pr_err("Stack dump where RCU GP kthread last ran:\n"); > >> + dump_cpu_task(cpu); > >> } > >> wake_up_process(gpk); > >> } > >> -- > >> 2.25.1 > >> > > . > > > > -- > Regards, > Zhen Lei
On 2023/7/12 0:48, Paul E. McKenney wrote: > On Tue, Jul 11, 2023 at 11:20:07AM +0800, Leizhen (ThunderTown) wrote: >> >> >> On 2023/7/11 3:03, Paul E. McKenney wrote: >>> On Wed, Jul 05, 2023 at 03:30:19PM +0800, Zhen Lei wrote: >>>> The above condition "if (gpk)" already ensures that gp_kthread is created, >>>> so the local variable 'cpu' cannot be negative here. >>>> >>>> Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> >>>> --- >>>> kernel/rcu/tree_stall.h | 12 +++++------- >>>> 1 file changed, 5 insertions(+), 7 deletions(-) >>>> >>>> diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h >>>> index b10b8349bb2a48b..dcfaa3d5db2cbc7 100644 >>>> --- a/kernel/rcu/tree_stall.h >>>> +++ b/kernel/rcu/tree_stall.h >>>> @@ -537,13 +537,11 @@ static void rcu_check_gp_kthread_starvation(void) >>>> pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); >>>> pr_err("RCU grace-period kthread stack dump:\n"); >>>> sched_show_task(gpk); >>>> - if (cpu >= 0) { >>> >>> I am not quite this trusting of the relation between the relationship >>> between the existence of the grace-period khread and its CPU number >>> being in range. Let's please start with something like this: >>> >>> if (!WARN_ON_ONCE(cpu < 0)) { >>> >>> Please note that this is not just me. See for example the use of the >>> cpumask_check() function, albeit the opposite concern. >> >> git grep -wn "\->cpu" kernel/ include/ >> kernel/kthread.c:583: to_kthread(p)->cpu = cpu; //kthread_create_on_cpu() >> kernel/sched/sched.h:2024: WRITE_ONCE(task_thread_info(p)->cpu, cpu); //__set_task_cpu() >> include/linux/sched.h:2250: return READ_ONCE(task_thread_info(p)->cpu); //task_cpu() >> >> git grep -wn "\.cpu" kernel/ include/ //There is no task related, the search result is omitted. >> >> Therefore, there is only one path "set_task_cpu()-->__set_task_cpu()" that can dynamically >> change the value of task_cpu(p). In fact, this guarantee has been made in set_task_cpu(). >> set_task_cpu >> WARN_ON_ONCE(!cpu_online(new_cpu)); >> __set_task_cpu(p, new_cpu); >> >> In addition, task_struct has member 'on_rq'. Therefore, when a task leaves the scheduling >> queue, setting the member 'cpu' to an invalid value will be thankless. > > Thank you for digging into this! Given that, as you say, we can dispense > with the check. > >> Sorry, these two patches was posted too quickly, and I'm still regretting that I should have >> attached this to the commit description these days. > > Please do resend the patches with this explanation in the commit log. > And please don't worry about making the English pretty, as I can always > wordsmith. OK, thank you very much. > > Thanx, Paul > >>>> - if (cpu_is_offline(cpu)) { >>>> - pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); >>>> - } else { >>>> - pr_err("Stack dump where RCU GP kthread last ran:\n"); >>>> - dump_cpu_task(cpu); >>>> - } >>>> + if (cpu_is_offline(cpu)) { >>>> + pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); >>>> + } else { >>>> + pr_err("Stack dump where RCU GP kthread last ran:\n"); >>>> + dump_cpu_task(cpu); >>>> } >>>> wake_up_process(gpk); >>>> } >>>> -- >>>> 2.25.1 >>>> >>> . >>> >> >> -- >> Regards, >> Zhen Lei > . >
diff --git a/kernel/rcu/tree_stall.h b/kernel/rcu/tree_stall.h index b10b8349bb2a48b..dcfaa3d5db2cbc7 100644 --- a/kernel/rcu/tree_stall.h +++ b/kernel/rcu/tree_stall.h @@ -537,13 +537,11 @@ static void rcu_check_gp_kthread_starvation(void) pr_err("\tUnless %s kthread gets sufficient CPU time, OOM is now expected behavior.\n", rcu_state.name); pr_err("RCU grace-period kthread stack dump:\n"); sched_show_task(gpk); - if (cpu >= 0) { - if (cpu_is_offline(cpu)) { - pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); - } else { - pr_err("Stack dump where RCU GP kthread last ran:\n"); - dump_cpu_task(cpu); - } + if (cpu_is_offline(cpu)) { + pr_err("RCU GP kthread last ran on offline CPU %d.\n", cpu); + } else { + pr_err("Stack dump where RCU GP kthread last ran:\n"); + dump_cpu_task(cpu); } wake_up_process(gpk); }
The above condition "if (gpk)" already ensures that gp_kthread is created, so the local variable 'cpu' cannot be negative here. Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com> --- kernel/rcu/tree_stall.h | 12 +++++------- 1 file changed, 5 insertions(+), 7 deletions(-)