[PATCH] stop_machine: call rcu_momentary_dyntick_idle() from irq disable path

From: Mukesh Ojha
Date: Tue Apr 09 2024 - 04:02:58 EST

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Next in thread: Paul E. McKenney: "Re: [PATCH] stop_machine: call rcu_momentary_dyntick_idle() from irq disable path"
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rcu_momentary_dyntick_idle() is getting called from all the irq
disable path(also documented in rcu_momentary_dyntick_idle())
however, in multi_cpu_stop() it is not.

"

* Let the RCU core know that this CPU has gone through the scheduler,
* which is a quiescent state. This is called when the need for a
* quiescent state is urgent, so we burn an atomic operation and full
* memory barriers to let the RCU core know about it, regardless of what
* this CPU might (or might not) do in the near future.
*
* We inform the RCU core by emulating a zero-duration dyntick-idle period.
*
* The caller must have disabled interrupts and must not be idle.

"

Let's fix this as it is possible that during stop_machine() call for
a kprobe registration[1] can get stuck when one cpu(cpu4) calls
rcu_momentary_dyntick_idle() after acking MULTI_STOP_PREPARE state[2]
and other cpus have acked MULTI_STOP_DISABLE_IRQ and waiting for earlier
cpu to reach to next state [3].

[1]

[<ffffffdb78c75c54>] __switch_to+0x1e8
[<ffffffdb78c76520>] __schedule+0x6bc
[<ffffffdb78c76af0>] preempt_schedule_common+0xb4
[<ffffffdb78c75e60>] preempt_schedule[jt]+0x20
[<ffffffdb77dd7bd0>] queue_stop_cpus_work[jt]+0xdc
[<ffffffdb77dd781c>] stop_machine_cpuslocked+0xdc
[<ffffffdb78c816f8>] aarch64_insn_patch_text[jt]+0x4c
[<ffffffdb78c81938>] arch_arm_kprobe+0x40
[<ffffffdb77de88c0>] arm_kprobe+0x3c
[<ffffffdb77de84f4>] register_kprobe+0x3fc

[2]
000|check_preemption_disabled(what1 = 0xFFFFFFDB79153D0B, what2 = 0xFFFFFFDB7912A911)
| what1 = 0xFFFFFFDB79153D0B
| what2 = 0xFFFFFFDB7912A911
-001|__this_cpu_preempt_check(op = ?)
-002|rcu_preempt_need_deferred_qs(inline)
| t = 0xFFFFFF8806879F80
| pscr_ret__ = 0
-002|rcu_preempt_deferred_qs(inline)
| t = 0xFFFFFF8806879F80
| flags = 0
-002|rcu_momentary_dyntick_idle()
-003|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_PREPARE ==> This seems to have acked MULTI_STOP_PREPARE
state and calls rcu_momentary_dyntick_idle()
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-004|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6D812F28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-005|smpboot_thread_fn(:data = 0xFFFFFF8805C063C0)
| data = 0xFFFFFF8805C063C0
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-006|kthread(_create = 0xFFFFFF8806B7EC00)
| _create = 0xFFFFFF8806B7EC00
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C063C0
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806402F00
| done = 0xFFFFFFC08005BA98
-007|ret_from_fork(asm)

[3]
000|touch_softlockup_watchdog()
-001|touch_nmi_watchdog(inline)
-001|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_DISABLE_IRQ
| newstate = MULTI_STOP_DISABLE_IRQ
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-002|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6D04EF28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-003|smpboot_thread_fn(:data = 0xFFFFFF8805C06230)
| data = 0xFFFFFF8805C06230
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-004|kthread(_create = 0xFFFFFF8806469D80)
| _create = 0xFFFFFF8806469D80
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C06230
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806401500
| done = 0xFFFFFFC08005B888
-005|ret_from_fork(asm)
---|end of frame

cpu1:

-000|touch_softlockup_watchdog()
-001|touch_nmi_watchdog(inline)
-001|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_DISABLE_IRQ
| newstate = MULTI_STOP_DISABLE_IRQ
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-002|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6D23FF28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-003|smpboot_thread_fn(:data = 0xFFFFFF8805C06270)
| data = 0xFFFFFF8805C06270
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-004|kthread(_create = 0xFFFFFF88066119C0)
| _create = 0xFFFFFF88066119C0
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C06270
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806401000
| done = 0xFFFFFFC08005BA98
-005|ret_from_fork(asm)
---|end of frame

cpu2:

-000|touch_softlockup_watchdog()
-001|touch_nmi_watchdog(inline)
-001|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_DISABLE_IRQ
| newstate = MULTI_STOP_DISABLE_IRQ
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-002|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6D430F28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-003|smpboot_thread_fn(:data = 0xFFFFFF8805C062E0)
| data = 0xFFFFFF8805C062E0
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-004|kthread(_create = 0xFFFFFF88067D5B80)
| _create = 0xFFFFFF88067D5B80
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C062E0
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806403F00
| done = 0xFFFFFFC08005BA98
-005|ret_from_fork(asm)
---|end of frame

cpu3:

-000|touch_softlockup_watchdog_sched(inline)
| __ptr = 18446743916840366040
-000|touch_softlockup_watchdog()
-001|touch_nmi_watchdog(inline)
-001|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_DISABLE_IRQ
| newstate = MULTI_STOP_DISABLE_IRQ
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-002|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6D621F28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-003|smpboot_thread_fn(:data = 0xFFFFFF8805C06350)
| data = 0xFFFFFF8805C06350
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-004|kthread(_create = 0xFFFFFF88069E7300)
| _create = 0xFFFFFF88069E7300
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C06350
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806403300
| done = 0xFFFFFFC08005BA98
-005|ret_from_fork(asm)
---|end of frame

Cpu5:

-000|check_preemption_disabled(what1 = ?, what2 = ?)
| what1 = ?
| what2 = ?
-001|debug_smp_processor_id()
-002|ct_state_inc(inline)
| incby = 8
| __ptr = 0
-002|rcu_momentary_dyntick_idle()
| seq = 0
-003|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_DISABLE_IRQ
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-004|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6DA03F28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-005|smpboot_thread_fn(:data = 0xFFFFFF8805C06430)
| data = 0xFFFFFF8805C06430
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-006|kthread(_create = 0xFFFFFF8806D58180)
| _create = 0xFFFFFF8806D58180
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C06430
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806402400
| done = 0xFFFFFFC08005BA98
-007|ret_from_fork(asm)
---|end of frame

Cpu6:

-000|check_preemption_disabled(what1 = ?, what2 = ?)
| what1 = ?
| what2 = ?
-001|__this_cpu_preempt_check(op = ?)
-002|rcu_preempt_need_deferred_qs(inline)
| t = 0xFFFFFF8806E03F00
| pscr_ret__ = 0
-002|rcu_preempt_deferred_qs(inline)
| t = 0xFFFFFF8806E03F00
| flags = 0
-002|rcu_momentary_dyntick_idle()
-003|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_DISABLE_IRQ
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-004|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6DBF4F28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-005|smpboot_thread_fn(:data = 0xFFFFFF8805C064A0)
| data = 0xFFFFFF8805C064A0
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-006|kthread(_create = 0xFFFFFF8806F67D00)
| _create = 0xFFFFFF8806F67D00
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C064A0
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806402600
| done = 0xFFFFFFC08005BA98
-007|ret_from_fork(asm)
---|end of frame

Cpu7:

-000|check_preemption_disabled(what1 = ?, what2 = ?)
| what1 = ?
| what2 = ?
-001|__this_cpu_preempt_check(op = ?)
-002|rcu_preempt_need_deferred_qs(inline)
| t = 0xFFFFFF8806E1DE80
| pscr_ret__ = 0
-002|rcu_preempt_deferred_qs(inline)
| t = 0xFFFFFF8806E1DE80
| flags = 0
-002|rcu_momentary_dyntick_idle()
-003|multi_cpu_stop(:data = 0xFFFFFFC084343478)
| data = 0xFFFFFFC084343478
| msdata = 0x0
| curstate = MULTI_STOP_DISABLE_IRQ
| flags = 0
| is_active = TRUE
| cpumask = 0xFFFFFFDB79E37718
| err = 0
-004|cpu_stopper_thread(cpu = ?)
| cpu = ?
| __already_done = FALSE
| stopper = 0xFFFFFF8B6DDE5F28
| fn = 0xFFFFFFDB77DD74C4
| arg = 0xFFFFFFC084343478
| done = 0xFFFFFFC0843434A0
| ret = ???
-005|smpboot_thread_fn(:data = 0xFFFFFF8805C06510)
| data = 0xFFFFFF8805C06510
| td = 0x0
| ht = 0xFFFFFFDB79EE8B40
-006|kthread(_create = 0xFFFFFF88070FF300)
| _create = 0xFFFFFF88070FF300
| param = (sched_priority = 0)
| create = 0x0
| data = 0xFFFFFF8805C06510
| threadfn = 0x0
| ret = ???
| self = 0xFFFFFF8806407D00
| done = 0xFFFFFFC08005BA98
-007|ret_from_fork(asm)
---|end of frame

Signed-off-by: Mukesh Ojha <quic_mojha@xxxxxxxxxxx>
---
kernel/stop_machine.c | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/kernel/stop_machine.c b/kernel/stop_machine.c
index cedb17ba158a..f93e6deb8150 100644
--- a/kernel/stop_machine.c
+++ b/kernel/stop_machine.c
@@ -250,8 +250,8 @@ static int multi_cpu_stop(void *data)
* be detected and reported on their side.
*/
touch_nmi_watchdog();
+ rcu_momentary_dyntick_idle();
}
- rcu_momentary_dyntick_idle();
} while (curstate != MULTI_STOP_EXIT);

local_irq_restore(flags);
--
2.7.4

Next message: Linux regression tracking (Thorsten Leemhuis): "Re: Fwd: Steam Deck OLED 6.8.2 nau8821-max fails"
Previous message: Oleksij Rempel: "Re: [PATCH net-next v4 6/9] net: dsa: microchip: dcb: add special handling for KSZ88X3 family"
Next in thread: Paul E. McKenney: "Re: [PATCH] stop_machine: call rcu_momentary_dyntick_idle() from irq disable path"
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