Re: [PATCH v13 00/12] support "task_isolation" mode

[Christoph Lameter]

We are trying to test the patchset on x86 and are getting strange
backtraces and aborts. It seems that the cpu before the cpu we are running
on creates an irq_work event that causes a latency event on the next cpu.

This is weird. Is there a new round robin IPI feature in the kernel that I
am not aware of?

Backtraces from dmesg:

[  956.603223] latencytest/7928: task_isolation mode lost due to irq_work
[  956.610817] cpu 12: irq_work violating task isolation for latencytest/7928 on cpu 13
[  956.619985] CPU: 12 PID: 0 Comm: swapper/12 Not tainted 4.7.0-rc7-stream1 #1
[  956.628765] Hardware name: Dell Inc. PowerEdge R630/0CNCJW, BIOS 2.0.2 03/15/2016
[  956.637642]  0000000000000086 ce6735c7b39e7b81 ffff88103e783d00 ffffffff8134f6ff
[  956.646739]  ffff88102c50d700 000000000000000d ffff88103e783d28 ffffffff811986f4
[  956.655828]  ffff88102c50d700 ffff88203cf97f80 000000000000000d ffff88103e783d68
[  956.664924] Call Trace:
[  956.667945]  <IRQ>  [<ffffffff8134f6ff>] dump_stack+0x63/0x84
[  956.674740]  [<ffffffff811986f4>] task_isolation_debug_task+0xb4/0xd0
[  956.682229]  [<ffffffff810b4a13>] _task_isolation_debug+0x83/0xc0
[  956.689331]  [<ffffffff81179c0c>] irq_work_queue_on+0x9c/0x120
[  956.696142]  [<ffffffff811075e4>] tick_nohz_full_kick_cpu+0x44/0x50
[  956.703438]  [<ffffffff810b48d9>] wake_up_nohz_cpu+0x99/0x110
[  956.710150]  [<ffffffff810f57e1>] internal_add_timer+0x71/0xb0
[  956.716959]  [<ffffffff810f696b>] add_timer_on+0xbb/0x140
[  956.723283]  [<ffffffff81100ca0>] clocksource_watchdog+0x230/0x300
[  956.730480]  [<ffffffff81100a70>] ? __clocksource_unstable.isra.2+0x40/0x40
[  956.738555]  [<ffffffff810f5615>] call_timer_fn+0x35/0x120
[  956.744973]  [<ffffffff81100a70>] ? __clocksource_unstable.isra.2+0x40/0x40
[  956.753046]  [<ffffffff810f64cc>] run_timer_softirq+0x23c/0x2f0
[  956.759952]  [<ffffffff816d4397>] __do_softirq+0xd7/0x2c5
[  956.766272]  [<ffffffff81091245>] irq_exit+0xf5/0x100
[  956.772209]  [<ffffffff816d41d2>] smp_apic_timer_interrupt+0x42/0x50
[  956.779600]  [<ffffffff816d231c>] apic_timer_interrupt+0x8c/0xa0
[  956.786602]  <EOI>  [<ffffffff81569eb0>] ? poll_idle+0x40/0x80
[  956.793490]  [<ffffffff815697dc>] cpuidle_enter_state+0x9c/0x260
[  956.800498]  [<ffffffff815699d7>] cpuidle_enter+0x17/0x20
[  956.806810]  [<ffffffff810cf497>] cpu_startup_entry+0x2b7/0x3a0
[  956.813717]  [<ffffffff81050e6c>] start_secondary+0x15c/0x1a0
[ 1036.601758] cpu 12: irq_work violating task isolation for latencytest/8447 on cpu 13
[ 1036.610922] CPU: 12 PID: 0 Comm: swapper/12 Not tainted 4.7.0-rc7-stream1 #1
[ 1036.619692] Hardware name: Dell Inc. PowerEdge R630/0CNCJW, BIOS 2.0.2 03/15/2016
[ 1036.628551]  0000000000000086 ce6735c7b39e7b81 ffff88103e783d00 ffffffff8134f6ff
[ 1036.637648]  ffff88102dca0000 000000000000000d ffff88103e783d28 ffffffff811986f4
[ 1036.646741]  ffff88102dca0000 ffff88203cf97f80 000000000000000d ffff88103e783d68
[ 1036.655833] Call Trace:
[ 1036.658852]  <IRQ>  [<ffffffff8134f6ff>] dump_stack+0x63/0x84
[ 1036.665649]  [<ffffffff811986f4>] task_isolation_debug_task+0xb4/0xd0
[ 1036.673136]  [<ffffffff810b4a13>] _task_isolation_debug+0x83/0xc0
[ 1036.680237]  [<ffffffff81179c0c>] irq_work_queue_on+0x9c/0x120
[ 1036.687091]  [<ffffffff811075e4>] tick_nohz_full_kick_cpu+0x44/0x50
[ 1036.694388]  [<ffffffff810b48d9>] wake_up_nohz_cpu+0x99/0x110
[ 1036.701089]  [<ffffffff810f57e1>] internal_add_timer+0x71/0xb0
[ 1036.707896]  [<ffffffff810f696b>] add_timer_on+0xbb/0x140
[ 1036.714210]  [<ffffffff81100ca0>] clocksource_watchdog+0x230/0x300
[ 1036.721411]  [<ffffffff81100a70>] ? __clocksource_unstable.isra.2+0x40/0x40
[ 1036.729478]  [<ffffffff810f5615>] call_timer_fn+0x35/0x120
[ 1036.735899]  [<ffffffff81100a70>] ? __clocksource_unstable.isra.2+0x40/0x40
[ 1036.743970]  [<ffffffff810f64cc>] run_timer_softirq+0x23c/0x2f0
[ 1036.750878]  [<ffffffff816d4397>] __do_softirq+0xd7/0x2c5
[ 1036.757199]  [<ffffffff81091245>] irq_exit+0xf5/0x100
[ 1036.763132]  [<ffffffff816d41d2>] smp_apic_timer_interrupt+0x42/0x50
[ 1036.770520]  [<ffffffff816d231c>] apic_timer_interrupt+0x8c/0xa0
[ 1036.777520]  <EOI>  [<ffffffff81569eb0>] ? poll_idle+0x40/0x80
[ 1036.784410]  [<ffffffff815697dc>] cpuidle_enter_state+0x9c/0x260
[ 1036.791413]  [<ffffffff815699d7>] cpuidle_enter+0x17/0x20
[ 1036.797734]  [<ffffffff810cf497>] cpu_startup_entry+0x2b7/0x3a0
[ 1036.804641]  [<ffffffff81050e6c>] start_secondary+0x15c/0x1a0