linux-toradex.git/kernel/softirq.c, branch v6.11-rc3 Linux kernel for Apalis and Colibri modules softirq: Fix suspicious RCU usage in __do_softirq() 2024-04-29T03:03:51+00:00 Zqiang qiang.zhang1211@gmail.com 2024-04-27T10:28:08+00:00 1dd1eff161bd55968d3d46bc36def62d71fb4785 Currently, the condition "__this_cpu_read(ksoftirqd) == current" is used to invoke rcu_softirq_qs() in ksoftirqd tasks context for non-RT kernels. This works correctly as long as the context is actually task context but this condition is wrong when: - the current task is ksoftirqd - the task is interrupted in a RCU read side critical section - __do_softirq() is invoked on return from interrupt Syzkaller triggered the following scenario: -> finish_task_switch() -> put_task_struct_rcu_user() -> call_rcu(&task->rcu, delayed_put_task_struct) -> __kasan_record_aux_stack() -> pfn_valid() -> rcu_read_lock_sched() <interrupt> __irq_exit_rcu() -> __do_softirq)() -> if (!IS_ENABLED(CONFIG_PREEMPT_RT) && __this_cpu_read(ksoftirqd) == current) -> rcu_softirq_qs() -> RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map)) The rcu quiescent state is reported in the rcu-read critical section, so the lockdep warning is triggered. Fix this by splitting out the inner working of __do_softirq() into a helper function which takes an argument to distinguish between ksoftirqd task context and interrupted context and invoke it from the relevant call sites with the proper context information and use that for the conditional invocation of rcu_softirq_qs(). Reported-by: syzbot+dce04ed6d1438ad69656@syzkaller.appspotmail.com Suggested-by: Thomas Gleixner <tglx@linutronix.de> Signed-off-by: Zqiang <qiang.zhang1211@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20240427102808.29356-1-qiang.zhang1211@gmail.com Link: https://lore.kernel.org/lkml/8f281a10-b85a-4586-9586-5bbc12dc784f@paulmck-laptop/T/#mea8aba4abfcb97bbf499d169ce7f30c4cff1b0e3 
Currently, the condition "__this_cpu_read(ksoftirqd) == current" is used to
invoke rcu_softirq_qs() in ksoftirqd tasks context for non-RT kernels.

This works correctly as long as the context is actually task context but
this condition is wrong when:

     - the current task is ksoftirqd
     - the task is interrupted in a RCU read side critical section
     - __do_softirq() is invoked on return from interrupt

Syzkaller triggered the following scenario:

  -> finish_task_switch()
    -> put_task_struct_rcu_user()
      -> call_rcu(&task->rcu, delayed_put_task_struct)
        -> __kasan_record_aux_stack()
          -> pfn_valid()
            -> rcu_read_lock_sched()
              <interrupt>
                __irq_exit_rcu()
                -> __do_softirq)()
                   -> if (!IS_ENABLED(CONFIG_PREEMPT_RT) &&
                     __this_cpu_read(ksoftirqd) == current)
                     -> rcu_softirq_qs()
                       -> RCU_LOCKDEP_WARN(lock_is_held(&rcu_sched_lock_map))

The rcu quiescent state is reported in the rcu-read critical section, so
the lockdep warning is triggered.

Fix this by splitting out the inner working of __do_softirq() into a helper
function which takes an argument to distinguish between ksoftirqd task
context and interrupted context and invoke it from the relevant call sites
with the proper context information and use that for the conditional
invocation of rcu_softirq_qs().

Reported-by: syzbot+dce04ed6d1438ad69656@syzkaller.appspotmail.com
Suggested-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20240427102808.29356-1-qiang.zhang1211@gmail.com
Link: https://lore.kernel.org/lkml/8f281a10-b85a-4586-9586-5bbc12dc784f@paulmck-laptop/T/#mea8aba4abfcb97bbf499d169ce7f30c4cff1b0e3
workqueue: Drain BH work items on hot-unplugged CPUs 2024-02-29T21:51:24+00:00 Tejun Heo tj@kernel.org 2024-02-27T01:38:55+00:00 1acd92d95fa24edca8f0292b21870025da93e24f Boqun pointed out that workqueues aren't handling BH work items on offlined CPUs. Unlike tasklet which transfers out the pending tasks from CPUHP_SOFTIRQ_DEAD, BH workqueue would just leave them pending which is problematic. Note that this behavior is specific to BH workqueues as the non-BH per-CPU workers just become unbound when the CPU goes offline. This patch fixes the issue by draining the pending BH work items from an offlined CPU from CPUHP_SOFTIRQ_DEAD. Because work items carry more context, it's not as easy to transfer the pending work items from one pool to another. Instead, run BH work items which execute the offlined pools on an online CPU. Note that this assumes that no further BH work items will be queued on the offlined CPUs. This assumption is shared with tasklet and should be fine for conversions. However, this issue also exists for per-CPU workqueues which will just keep executing work items queued after CPU offline on unbound workers and workqueue should reject per-CPU and BH work items queued on offline CPUs. This will be addressed separately later. Signed-off-by: Tejun Heo <tj@kernel.org> Reported-and-reviewed-by: Boqun Feng <boqun.feng@gmail.com> Link: http://lkml.kernel.org/r/Zdvw0HdSXcU3JZ4g@boqun-archlinux 
Boqun pointed out that workqueues aren't handling BH work items on offlined
CPUs. Unlike tasklet which transfers out the pending tasks from
CPUHP_SOFTIRQ_DEAD, BH workqueue would just leave them pending which is
problematic. Note that this behavior is specific to BH workqueues as the
non-BH per-CPU workers just become unbound when the CPU goes offline.

This patch fixes the issue by draining the pending BH work items from an
offlined CPU from CPUHP_SOFTIRQ_DEAD. Because work items carry more context,
it's not as easy to transfer the pending work items from one pool to
another. Instead, run BH work items which execute the offlined pools on an
online CPU.

Note that this assumes that no further BH work items will be queued on the
offlined CPUs. This assumption is shared with tasklet and should be fine for
conversions. However, this issue also exists for per-CPU workqueues which
will just keep executing work items queued after CPU offline on unbound
workers and workqueue should reject per-CPU and BH work items queued on
offline CPUs. This will be addressed separately later.

Signed-off-by: Tejun Heo <tj@kernel.org>
Reported-and-reviewed-by: Boqun Feng <boqun.feng@gmail.com>
Link: http://lkml.kernel.org/r/Zdvw0HdSXcU3JZ4g@boqun-archlinux
workqueue: Implement BH workqueues to eventually replace tasklets 2024-02-04T21:28:06+00:00 Tejun Heo tj@kernel.org 2024-02-04T21:28:06+00:00 4cb1ef64609f9b0254184b2947824f4b46ccab22 The only generic interface to execute asynchronously in the BH context is tasklet; however, it's marked deprecated and has some design flaws such as the execution code accessing the tasklet item after the execution is complete which can lead to subtle use-after-free in certain usage scenarios and less-developed flush and cancel mechanisms. This patch implements BH workqueues which share the same semantics and features of regular workqueues but execute their work items in the softirq context. As there is always only one BH execution context per CPU, none of the concurrency management mechanisms applies and a BH workqueue can be thought of as a convenience wrapper around softirq. Except for the inability to sleep while executing and lack of max_active adjustments, BH workqueues and work items should behave the same as regular workqueues and work items. Currently, the execution is hooked to tasklet[_hi]. However, the goal is to convert all tasklet users over to BH workqueues. Once the conversion is complete, tasklet can be removed and BH workqueues can directly take over the tasklet softirqs. system_bh[_highpri]_wq are added. As queue-wide flushing doesn't exist in tasklet, all existing tasklet users should be able to use the system BH workqueues without creating their own workqueues. v3: - Add missing interrupt.h include. v2: - Instead of using tasklets, hook directly into its softirq action functions - tasklet[_hi]_action(). This is slightly cheaper and closer to the eventual code structure we want to arrive at. Suggested by Lai. - Lai also pointed out several places which need NULL worker->task handling or can use clarification. Updated. Signed-off-by: Tejun Heo <tj@kernel.org> Suggested-by: Linus Torvalds <torvalds@linux-foundation.org> Link: http://lkml.kernel.org/r/CAHk-=wjDW53w4-YcSmgKC5RruiRLHmJ1sXeYdp_ZgVoBw=5byA@mail.gmail.com Tested-by: Allen Pais <allen.lkml@gmail.com> Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com> 
The only generic interface to execute asynchronously in the BH context is
tasklet; however, it's marked deprecated and has some design flaws such as
the execution code accessing the tasklet item after the execution is
complete which can lead to subtle use-after-free in certain usage scenarios
and less-developed flush and cancel mechanisms.

This patch implements BH workqueues which share the same semantics and
features of regular workqueues but execute their work items in the softirq
context. As there is always only one BH execution context per CPU, none of
the concurrency management mechanisms applies and a BH workqueue can be
thought of as a convenience wrapper around softirq.

Except for the inability to sleep while executing and lack of max_active
adjustments, BH workqueues and work items should behave the same as regular
workqueues and work items.

Currently, the execution is hooked to tasklet[_hi]. However, the goal is to
convert all tasklet users over to BH workqueues. Once the conversion is
complete, tasklet can be removed and BH workqueues can directly take over
the tasklet softirqs.

system_bh[_highpri]_wq are added. As queue-wide flushing doesn't exist in
tasklet, all existing tasklet users should be able to use the system BH
workqueues without creating their own workqueues.

v3: - Add missing interrupt.h include.

v2: - Instead of using tasklets, hook directly into its softirq action
      functions - tasklet[_hi]_action(). This is slightly cheaper and closer
      to the eventual code structure we want to arrive at. Suggested by Lai.

    - Lai also pointed out several places which need NULL worker->task
      handling or can use clarification. Updated.

Signed-off-by: Tejun Heo <tj@kernel.org>
Suggested-by: Linus Torvalds <torvalds@linux-foundation.org>
Link: http://lkml.kernel.org/r/CAHk-=wjDW53w4-YcSmgKC5RruiRLHmJ1sXeYdp_ZgVoBw=5byA@mail.gmail.com
Tested-by: Allen Pais <allen.lkml@gmail.com>
Reviewed-by: Lai Jiangshan <jiangshanlai@gmail.com>
sched/core: introduce sched_core_idle_cpu() 2023-07-13T13:21:50+00:00 Cruz Zhao CruzZhao@linux.alibaba.com 2023-06-29T04:02:04+00:00 548796e2e70b44b4661fd7feee6eb239245ff1f8 As core scheduling introduced, a new state of idle is defined as force idle, running idle task but nr_running greater than zero. If a cpu is in force idle state, idle_cpu() will return zero. This result makes sense in some scenarios, e.g., load balance, showacpu when dumping, and judge the RCU boost kthread is starving. But this will cause error in other scenarios, e.g., tick_irq_exit(): When force idle, rq->curr == rq->idle but rq->nr_running > 0, results that idle_cpu() returns 0. In function tick_irq_exit(), if idle_cpu() is 0, tick_nohz_irq_exit() will not be called, and ts->idle_active will not become 1, which became 0 in tick_nohz_irq_enter(). ts->idle_sleeptime won't update in function update_ts_time_stats(), if ts->idle_active is 0, which should be 1. And this bug will result that ts->idle_sleeptime is less than the actual value, and finally will result that the idle time in /proc/stat is less than the actual value. To solve this problem, we introduce sched_core_idle_cpu(), which returns 1 when force idle. We audit all users of idle_cpu(), and change idle_cpu() into sched_core_idle_cpu() in function tick_irq_exit(). v2-->v3: Only replace idle_cpu() with sched_core_idle_cpu() in function tick_irq_exit(). And modify the corresponding commit log. Signed-off-by: Cruz Zhao <CruzZhao@linux.alibaba.com> Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org> Reviewed-by: Peter Zijlstra <peterz@infradead.org> Reviewed-by: Frederic Weisbecker <frederic@kernel.org> Reviewed-by: Joel Fernandes <joel@joelfernandes.org> Link: https://lore.kernel.org/r/1688011324-42406-1-git-send-email-CruzZhao@linux.alibaba.com 
As core scheduling introduced, a new state of idle is defined as
force idle, running idle task but nr_running greater than zero.

If a cpu is in force idle state, idle_cpu() will return zero. This
result makes sense in some scenarios, e.g., load balance,
showacpu when dumping, and judge the RCU boost kthread is starving.

But this will cause error in other scenarios, e.g., tick_irq_exit():
When force idle, rq->curr == rq->idle but rq->nr_running > 0, results
that idle_cpu() returns 0. In function tick_irq_exit(), if idle_cpu()
is 0, tick_nohz_irq_exit() will not be called, and ts->idle_active will
not become 1, which became 0 in tick_nohz_irq_enter().
ts->idle_sleeptime won't update in function update_ts_time_stats(), if
ts->idle_active is 0, which should be 1. And this bug will result that
ts->idle_sleeptime is less than the actual value, and finally will
result that the idle time in /proc/stat is less than the actual value.

To solve this problem, we introduce sched_core_idle_cpu(), which
returns 1 when force idle. We audit all users of idle_cpu(), and
change idle_cpu() into sched_core_idle_cpu() in function
tick_irq_exit().

v2-->v3: Only replace idle_cpu() with sched_core_idle_cpu() in
function tick_irq_exit(). And modify the corresponding commit log.

Signed-off-by: Cruz Zhao <CruzZhao@linux.alibaba.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Reviewed-by: Peter Zijlstra <peterz@infradead.org>
Reviewed-by: Frederic Weisbecker <frederic@kernel.org>
Reviewed-by: Joel Fernandes <joel@joelfernandes.org>
Link: https://lore.kernel.org/r/1688011324-42406-1-git-send-email-CruzZhao@linux.alibaba.com
Revert "softirq: Let ksoftirqd do its job" 2023-05-09T19:50:27+00:00 Paolo Abeni pabeni@redhat.com 2023-05-08T06:17:44+00:00 d15121be7485655129101f3960ae6add40204463 This reverts the following commits: 4cd13c21b207 ("softirq: Let ksoftirqd do its job") 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous") 1342d8080f61 ("softirq: Don't skip softirq execution when softirq thread is parking") in a single change to avoid known bad intermediate states introduced by a patch series reverting them individually. Due to the mentioned commit, when the ksoftirqd threads take charge of softirq processing, the system can experience high latencies. In the past a few workarounds have been implemented for specific side-effects of the initial ksoftirqd enforcement commit: commit 1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not deferred") commit 8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do not get to run") commit 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()") commit 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous") But the latency problem still exists in real-life workloads, see the link below. The reverted commit intended to solve a live-lock scenario that can now be addressed with the NAPI threaded mode, introduced with commit 29863d41bb6e ("net: implement threaded-able napi poll loop support"), which is nowadays in a pretty stable status. While a complete solution to put softirq processing under nice resource control would be preferable, that has proven to be a very hard task. In the short term, remove the main pain point, and also simplify a bit the current softirq implementation. Signed-off-by: Paolo Abeni <pabeni@redhat.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Jason Xing <kerneljasonxing@gmail.com> Reviewed-by: Jakub Kicinski <kuba@kernel.org> Reviewed-by: Eric Dumazet <edumazet@google.com> Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Cc: "Paul E. McKenney" <paulmck@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: netdev@vger.kernel.org Link: https://lore.kernel.org/netdev/305d7742212cbe98621b16be782b0562f1012cb6.camel@redhat.com Link: https://lore.kernel.org/r/57e66b364f1b6f09c9bc0316742c3b14f4ce83bd.1683526542.git.pabeni@redhat.com 
This reverts the following commits:

  4cd13c21b207 ("softirq: Let ksoftirqd do its job")
  3c53776e29f8 ("Mark HI and TASKLET softirq synchronous")
  1342d8080f61 ("softirq: Don't skip softirq execution when softirq thread is parking")

in a single change to avoid known bad intermediate states introduced by a
patch series reverting them individually.

Due to the mentioned commit, when the ksoftirqd threads take charge of
softirq processing, the system can experience high latencies.

In the past a few workarounds have been implemented for specific
side-effects of the initial ksoftirqd enforcement commit:

commit 1ff688209e2e ("watchdog: core: make sure the watchdog_worker is not deferred")
commit 8d5755b3f77b ("watchdog: softdog: fire watchdog even if softirqs do not get to run")
commit 217f69743681 ("net: busy-poll: allow preemption in sk_busy_loop()")
commit 3c53776e29f8 ("Mark HI and TASKLET softirq synchronous")

But the latency problem still exists in real-life workloads, see the link
below.

The reverted commit intended to solve a live-lock scenario that can now be
addressed with the NAPI threaded mode, introduced with commit 29863d41bb6e
("net: implement threaded-able napi poll loop support"), which is nowadays
in a pretty stable status.

While a complete solution to put softirq processing under nice resource
control would be preferable, that has proven to be a very hard task. In
the short term, remove the main pain point, and also simplify a bit the
current softirq implementation.

Signed-off-by: Paolo Abeni <pabeni@redhat.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Jason Xing <kerneljasonxing@gmail.com>
Reviewed-by: Jakub Kicinski <kuba@kernel.org>
Reviewed-by: Eric Dumazet <edumazet@google.com>
Reviewed-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: netdev@vger.kernel.org
Link: https://lore.kernel.org/netdev/305d7742212cbe98621b16be782b0562f1012cb6.camel@redhat.com
Link: https://lore.kernel.org/r/57e66b364f1b6f09c9bc0316742c3b14f4ce83bd.1683526542.git.pabeni@redhat.com
softirq: Add trace points for tasklet entry/exit 2023-04-15T08:17:16+00:00 Lingutla Chandrasekhar clingutla@codeaurora.org 2023-04-07T23:05:26+00:00 f4bf3ca2e5cba655824b6e0893a98dfb33ed24e5 Tasklets are supposed to finish their work quickly and should not block the current running process, but it is not guaranteed that they do so. Currently softirq_entry/exit can be used to analyse the total tasklets execution time, but that's not helpful to track individual tasklets execution time. That makes it hard to identify tasklet functions, which take more time than expected. Add tasklet_entry/exit trace point support to track individual tasklet execution. Trivial usage example: # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_entry/enable # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_exit/enable # cat /sys/kernel/debug/tracing/trace # tracer: nop # # entries-in-buffer/entries-written: 4/4 #P:4 # # _-----=> irqs-off/BH-disabled # / _----=> need-resched # | / _---=> hardirq/softirq # || / _--=> preempt-depth # ||| / _-=> migrate-disable # |||| / delay # TASK-PID CPU# ||||| TIMESTAMP FUNCTION # | | | ||||| | | <idle>-0 [003] ..s1. 314.011428: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func <idle>-0 [003] ..s1. 314.011432: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func <idle>-0 [003] ..s1. 314.017369: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func <idle>-0 [003] ..s1. 314.017371: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org> Signed-off-by: J. Avila <elavila@google.com> Signed-off-by: John Stultz <jstultz@google.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org> Link: https://lore.kernel.org/r/20230407230526.1685443-1-jstultz@google.com [elavila: Port to android-mainline] [jstultz: Rebased to upstream, cut unused trace points, added comments for the tracepoints, reworded commit] 
Tasklets are supposed to finish their work quickly and should not block the
current running process, but it is not guaranteed that they do so.

Currently softirq_entry/exit can be used to analyse the total tasklets
execution time, but that's not helpful to track individual tasklets
execution time. That makes it hard to identify tasklet functions, which
take more time than expected.

Add tasklet_entry/exit trace point support to track individual tasklet
execution.

Trivial usage example:
   # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_entry/enable
   # echo 1 > /sys/kernel/debug/tracing/events/irq/tasklet_exit/enable
   # cat /sys/kernel/debug/tracing/trace
 # tracer: nop
 #
 # entries-in-buffer/entries-written: 4/4   #P:4
 #
 #                                _-----=> irqs-off/BH-disabled
 #                               / _----=> need-resched
 #                              | / _---=> hardirq/softirq
 #                              || / _--=> preempt-depth
 #                              ||| / _-=> migrate-disable
 #                              |||| /     delay
 #           TASK-PID     CPU#  |||||  TIMESTAMP  FUNCTION
 #              | |         |   |||||     |         |
           <idle>-0       [003] ..s1.   314.011428: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
           <idle>-0       [003] ..s1.   314.011432: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
           <idle>-0       [003] ..s1.   314.017369: tasklet_entry: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func
           <idle>-0       [003] ..s1.   314.017371: tasklet_exit: tasklet=0xffffa01ef8db2740 function=tcp_tasklet_func

Signed-off-by: Lingutla Chandrasekhar <clingutla@codeaurora.org>
Signed-off-by: J. Avila <elavila@google.com>
Signed-off-by: John Stultz <jstultz@google.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Steven Rostedt (Google) <rostedt@goodmis.org>
Link: https://lore.kernel.org/r/20230407230526.1685443-1-jstultz@google.com

[elavila: Port to android-mainline]
[jstultz: Rebased to upstream, cut unused trace points, added
 comments for the tracepoints, reworded commit]
context_tracking: Take IRQ eqs entrypoints over RCU 2022-07-05T20:32:59+00:00 Frederic Weisbecker frederic@kernel.org 2022-06-08T14:40:26+00:00 6f0e6c1598b1a3d19fc30db86b6e26d6f881b43d The RCU dynticks counter is going to be merged into the context tracking subsystem. Prepare with moving the IRQ extended quiescent states entrypoints to context tracking. For now those are dumb redirection to existing RCU calls. [ paulmck: Apply Stephen Rothwell feedback from -next. ] [ paulmck: Apply Nathan Chancellor feedback. ] Acked-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com> Cc: Uladzislau Rezki <uladzislau.rezki@sony.com> Cc: Joel Fernandes <joel@joelfernandes.org> Cc: Boqun Feng <boqun.feng@gmail.com> Cc: Nicolas Saenz Julienne <nsaenz@kernel.org> Cc: Marcelo Tosatti <mtosatti@redhat.com> Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com> Cc: Yu Liao <liaoyu15@huawei.com> Cc: Phil Auld <pauld@redhat.com> Cc: Paul Gortmaker<paul.gortmaker@windriver.com> Cc: Alex Belits <abelits@marvell.com> Signed-off-by: Paul E. McKenney <paulmck@kernel.org> Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com> Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com> 
The RCU dynticks counter is going to be merged into the context tracking
subsystem. Prepare with moving the IRQ extended quiescent states
entrypoints to context tracking. For now those are dumb redirection to
existing RCU calls.

[ paulmck: Apply Stephen Rothwell feedback from -next. ]
[ paulmck: Apply Nathan Chancellor feedback. ]

Acked-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Neeraj Upadhyay <quic_neeraju@quicinc.com>
Cc: Uladzislau Rezki <uladzislau.rezki@sony.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Nicolas Saenz Julienne <nsaenz@kernel.org>
Cc: Marcelo Tosatti <mtosatti@redhat.com>
Cc: Xiongfeng Wang <wangxiongfeng2@huawei.com>
Cc: Yu Liao <liaoyu15@huawei.com>
Cc: Phil Auld <pauld@redhat.com>
Cc: Paul Gortmaker<paul.gortmaker@windriver.com>
Cc: Alex Belits <abelits@marvell.com>
Signed-off-by: Paul E. McKenney <paulmck@kernel.org>
Reviewed-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
Tested-by: Nicolas Saenz Julienne <nsaenzju@redhat.com>
smp: Make softirq handling RT safe in flush_smp_call_function_queue() 2022-05-01T08:03:43+00:00 Sebastian Andrzej Siewior bigeasy@linutronix.de 2022-04-13T13:31:05+00:00 1a90bfd220201fbe050dfc15deaac20ca5f15638 flush_smp_call_function_queue() invokes do_softirq() which is not available on PREEMPT_RT. flush_smp_call_function_queue() is invoked from the idle task and the migration task with preemption or interrupts disabled. So RT kernels cannot process soft interrupts in that context as that has to acquire 'sleeping spinlocks' which is not possible with preemption or interrupts disabled and forbidden from the idle task anyway. The currently known SMP function call which raises a soft interrupt is in the block layer, but this functionality is not enabled on RT kernels due to latency and performance reasons. RT could wake up ksoftirqd unconditionally, but this wants to be avoided if there were soft interrupts pending already when this is invoked in the context of the migration task. The migration task might have preempted a threaded interrupt handler which raised a soft interrupt, but did not reach the local_bh_enable() to process it. The "running" ksoftirqd might prevent the handling in the interrupt thread context which is causing latency issues. Add a new function which handles this case explicitely for RT and falls back to do_softirq() on !RT kernels. In the RT case this warns when one of the flushed SMP function calls raised a soft interrupt so this can be investigated. [ tglx: Moved the RT part out of SMP code ] Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org> Link: https://lore.kernel.org/r/YgKgL6aPj8aBES6G@linutronix.de Link: https://lore.kernel.org/r/20220413133024.356509586@linutronix.de 
flush_smp_call_function_queue() invokes do_softirq() which is not available
on PREEMPT_RT. flush_smp_call_function_queue() is invoked from the idle
task and the migration task with preemption or interrupts disabled.

So RT kernels cannot process soft interrupts in that context as that has to
acquire 'sleeping spinlocks' which is not possible with preemption or
interrupts disabled and forbidden from the idle task anyway.

The currently known SMP function call which raises a soft interrupt is in
the block layer, but this functionality is not enabled on RT kernels due to
latency and performance reasons.

RT could wake up ksoftirqd unconditionally, but this wants to be avoided if
there were soft interrupts pending already when this is invoked in the
context of the migration task. The migration task might have preempted a
threaded interrupt handler which raised a soft interrupt, but did not reach
the local_bh_enable() to process it. The "running" ksoftirqd might prevent
the handling in the interrupt thread context which is causing latency
issues.

Add a new function which handles this case explicitely for RT and falls
back to do_softirq() on !RT kernels. In the RT case this warns when one of
the flushed SMP function calls raised a soft interrupt so this can be
investigated.

[ tglx: Moved the RT part out of SMP code ]

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Acked-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Link: https://lore.kernel.org/r/YgKgL6aPj8aBES6G@linutronix.de
Link: https://lore.kernel.org/r/20220413133024.356509586@linutronix.de
genirq, softirq: Use in_hardirq() instead of in_irq() 2022-02-02T20:34:19+00:00 Changbin Du changbin.du@gmail.com 2022-01-28T11:07:27+00:00 fe13889c390e14205e064d7e159e61eb5da4b1c3 Replace the obsolete and ambiguos macro in_irq() with the new macro in_hardirq(). Signed-off-by: Changbin Du <changbin.du@gmail.com> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Link: https://lore.kernel.org/r/20220128110727.5110-1-changbin.du@gmail.com 
Replace the obsolete and ambiguos macro in_irq() with the new macro
in_hardirq().

Signed-off-by: Changbin Du <changbin.du@gmail.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/r/20220128110727.5110-1-changbin.du@gmail.com
timers/nohz: Last resort update jiffies on nohz_full IRQ entry 2021-12-02T14:07:22+00:00 Frederic Weisbecker frederic@kernel.org 2021-10-26T14:10:54+00:00 53e87e3cdc155f20c3417b689df8d2ac88d79576 When at least one CPU runs in nohz_full mode, a dedicated timekeeper CPU is guaranteed to stay online and to never stop its tick. Meanwhile on some rare case, the dedicated timekeeper may be running with interrupts disabled for a while, such as in stop_machine. If jiffies stop being updated, a nohz_full CPU may end up endlessly programming the next tick in the past, taking the last jiffies update monotonic timestamp as a stale base, resulting in an tick storm. Here is a scenario where it matters: 0) CPU 0 is the timekeeper and CPU 1 a nohz_full CPU. 1) A stop machine callback is queued to execute somewhere. 2) CPU 0 reaches MULTI_STOP_DISABLE_IRQ while CPU 1 is still in MULTI_STOP_PREPARE. Hence CPU 0 can't do its timekeeping duty. CPU 1 can still take IRQs. 3) CPU 1 receives an IRQ which queues a timer callback one jiffy forward. 4) On IRQ exit, CPU 1 schedules the tick one jiffy forward, taking last_jiffies_update as a base. But last_jiffies_update hasn't been updated for 2 jiffies since the timekeeper has interrupts disabled. 5) clockevents_program_event(), which relies on ktime_get(), observes that the expiration is in the past and therefore programs the min delta event on the clock. 6) The tick fires immediately, goto 3) 7) Tick storm, the nohz_full CPU is drown and takes ages to reach MULTI_STOP_DISABLE_IRQ, which is the only way out of this situation. Solve this with unconditionally updating jiffies if the value is stale on nohz_full IRQ entry. IRQs and other disturbances are expected to be rare enough on nohz_full for the unconditional call to ktime_get() to actually matter. Reported-by: Paul E. McKenney <paulmck@kernel.org> Signed-off-by: Frederic Weisbecker <frederic@kernel.org> Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Tested-by: Paul E. McKenney <paulmck@kernel.org> Link: https://lore.kernel.org/r/20211026141055.57358-2-frederic@kernel.org 
When at least one CPU runs in nohz_full mode, a dedicated timekeeper CPU
is guaranteed to stay online and to never stop its tick.

Meanwhile on some rare case, the dedicated timekeeper may be running
with interrupts disabled for a while, such as in stop_machine.

If jiffies stop being updated, a nohz_full CPU may end up endlessly
programming the next tick in the past, taking the last jiffies update
monotonic timestamp as a stale base, resulting in an tick storm.

Here is a scenario where it matters:

0) CPU 0 is the timekeeper and CPU 1 a nohz_full CPU.

1) A stop machine callback is queued to execute somewhere.

2) CPU 0 reaches MULTI_STOP_DISABLE_IRQ while CPU 1 is still in
   MULTI_STOP_PREPARE. Hence CPU 0 can't do its timekeeping duty. CPU 1
   can still take IRQs.

3) CPU 1 receives an IRQ which queues a timer callback one jiffy forward.

4) On IRQ exit, CPU 1 schedules the tick one jiffy forward, taking
   last_jiffies_update as a base. But last_jiffies_update hasn't been
   updated for 2 jiffies since the timekeeper has interrupts disabled.

5) clockevents_program_event(), which relies on ktime_get(), observes
   that the expiration is in the past and therefore programs the min
   delta event on the clock.

6) The tick fires immediately, goto 3)

7) Tick storm, the nohz_full CPU is drown and takes ages to reach
   MULTI_STOP_DISABLE_IRQ, which is the only way out of this situation.

Solve this with unconditionally updating jiffies if the value is stale
on nohz_full IRQ entry. IRQs and other disturbances are expected to be
rare enough on nohz_full for the unconditional call to ktime_get() to
actually matter.

Reported-by: Paul E. McKenney <paulmck@kernel.org>
Signed-off-by: Frederic Weisbecker <frederic@kernel.org>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Tested-by: Paul E. McKenney <paulmck@kernel.org>
Link: https://lore.kernel.org/r/20211026141055.57358-2-frederic@kernel.org