| Message ID | 20210923140951.35902-3-kernelfans@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | watchdog_hld cleanup and async model for arm64 | expand |
On Thu 2021-09-23 22:09:49, Pingfan Liu wrote: > As for the context, there are two arguments to change > debug_smp_processor_id() to is_percpu_thread(). > > -1. watchdog_ev is percpu, and migration will frustrate the attempt > which try to bind a watchdog_ev to a cpu by protecting this func inside > the pair of preempt_disable()/preempt_enable(). > > -2. hardlockup_detector_event_create() indirectly calls > kmem_cache_alloc_node(), which is blockable. > > So here, spelling out the really planned context "is_percpu_thread()". The description is pretty hard to understand. I would suggest something like: Subject: kernel/watchdog_hld: Ensure CPU-bound context when creating hardlockup detector event hardlockup_detector_event_create() should create perf_event on the current CPU. Preemption could not get disabled because perf_event_create_kernel_counter() allocates memory. Instead, the CPU locality is achieved by processing the code in a per-CPU bound kthread. Add a check to prevent mistakes when calling the code in another code path. > Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > Cc: Petr Mladek <pmladek@suse.com> > Cc: Andrew Morton <akpm@linux-foundation.org> > Cc: Wang Qing <wangqing@vivo.com> > Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> > Cc: Santosh Sivaraj <santosh@fossix.org> > Cc: linux-arm-kernel@lists.infradead.org > To: linux-kernel@vger.kernel.org > --- > kernel/watchdog_hld.c | 5 ++++- > 1 file changed, 4 insertions(+), 1 deletion(-) > > diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c > index 247bf0b1582c..df010df76576 100644 > --- a/kernel/watchdog_hld.c > +++ b/kernel/watchdog_hld.c > @@ -165,10 +165,13 @@ static void watchdog_overflow_callback(struct perf_event *event, > > static int hardlockup_detector_event_create(void) > { > - unsigned int cpu = smp_processor_id(); > + unsigned int cpu; > struct perf_event_attr *wd_attr; > struct perf_event *evt; > > + /* This function plans to execute in cpu bound kthread */ This does not explain why it is needed. I suggest something like: /* * Preemption is not disabled because memory will be allocated. * Ensure CPU-locality by calling this in per-CPU kthread. */ > + WARN_ON(!is_percpu_thread()); > + cpu = raw_smp_processor_id(); > wd_attr = &wd_hw_attr; > wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh); > Othrewise the change looks good to me. Best Regards, Petr
On Mon, Oct 04, 2021 at 02:32:47PM +0200, Petr Mladek wrote: > On Thu 2021-09-23 22:09:49, Pingfan Liu wrote: > > As for the context, there are two arguments to change > > debug_smp_processor_id() to is_percpu_thread(). > > > > -1. watchdog_ev is percpu, and migration will frustrate the attempt > > which try to bind a watchdog_ev to a cpu by protecting this func inside > > the pair of preempt_disable()/preempt_enable(). > > > > -2. hardlockup_detector_event_create() indirectly calls > > kmem_cache_alloc_node(), which is blockable. > > > > So here, spelling out the really planned context "is_percpu_thread()". > > The description is pretty hard to understand. I would suggest > something like: > > Subject: kernel/watchdog_hld: Ensure CPU-bound context when creating > hardlockup detector event > > hardlockup_detector_event_create() should create perf_event on the > current CPU. Preemption could not get disabled because > perf_event_create_kernel_counter() allocates memory. Instead, > the CPU locality is achieved by processing the code in a per-CPU > bound kthread. > > Add a check to prevent mistakes when calling the code in another > code path. > Appreciate for that. I will use it. > > Signed-off-by: Pingfan Liu <kernelfans@gmail.com> > > Cc: Petr Mladek <pmladek@suse.com> > > Cc: Andrew Morton <akpm@linux-foundation.org> > > Cc: Wang Qing <wangqing@vivo.com> > > Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> > > Cc: Santosh Sivaraj <santosh@fossix.org> > > Cc: linux-arm-kernel@lists.infradead.org > > To: linux-kernel@vger.kernel.org > > --- > > kernel/watchdog_hld.c | 5 ++++- > > 1 file changed, 4 insertions(+), 1 deletion(-) > > > > diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c > > index 247bf0b1582c..df010df76576 100644 > > --- a/kernel/watchdog_hld.c > > +++ b/kernel/watchdog_hld.c > > @@ -165,10 +165,13 @@ static void watchdog_overflow_callback(struct perf_event *event, > > > > static int hardlockup_detector_event_create(void) > > { > > - unsigned int cpu = smp_processor_id(); > > + unsigned int cpu; > > struct perf_event_attr *wd_attr; > > struct perf_event *evt; > > > > + /* This function plans to execute in cpu bound kthread */ > > This does not explain why it is needed. I suggest something like: > > /* > * Preemption is not disabled because memory will be allocated. > * Ensure CPU-locality by calling this in per-CPU kthread. > */ > It sounds good. I will use it. > > > + WARN_ON(!is_percpu_thread()); > > + cpu = raw_smp_processor_id(); > > wd_attr = &wd_hw_attr; > > wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh); > > > > Othrewise the change looks good to me. > Thank for your help. Regards, Pingfan > > _______________________________________________ > linux-arm-kernel mailing list > linux-arm-kernel@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
diff --git a/kernel/watchdog_hld.c b/kernel/watchdog_hld.c index 247bf0b1582c..df010df76576 100644 --- a/kernel/watchdog_hld.c +++ b/kernel/watchdog_hld.c @@ -165,10 +165,13 @@ static void watchdog_overflow_callback(struct perf_event *event, static int hardlockup_detector_event_create(void) { - unsigned int cpu = smp_processor_id(); + unsigned int cpu; struct perf_event_attr *wd_attr; struct perf_event *evt; + /* This function plans to execute in cpu bound kthread */ + WARN_ON(!is_percpu_thread()); + cpu = raw_smp_processor_id(); wd_attr = &wd_hw_attr; wd_attr->sample_period = hw_nmi_get_sample_period(watchdog_thresh);
As for the context, there are two arguments to change debug_smp_processor_id() to is_percpu_thread(). -1. watchdog_ev is percpu, and migration will frustrate the attempt which try to bind a watchdog_ev to a cpu by protecting this func inside the pair of preempt_disable()/preempt_enable(). -2. hardlockup_detector_event_create() indirectly calls kmem_cache_alloc_node(), which is blockable. So here, spelling out the really planned context "is_percpu_thread()". Signed-off-by: Pingfan Liu <kernelfans@gmail.com> Cc: Petr Mladek <pmladek@suse.com> Cc: Andrew Morton <akpm@linux-foundation.org> Cc: Wang Qing <wangqing@vivo.com> Cc: "Peter Zijlstra (Intel)" <peterz@infradead.org> Cc: Santosh Sivaraj <santosh@fossix.org> Cc: linux-arm-kernel@lists.infradead.org To: linux-kernel@vger.kernel.org --- kernel/watchdog_hld.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-)