56 lines
1.6 KiB
ReStructuredText
56 lines
1.6 KiB
ReStructuredText
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Monitor wip
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===========
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- Name: wip - wakeup in preemptive
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- Type: per-cpu deterministic automaton
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- Author: Daniel Bristot de Oliveira <bristot@kernel.org>
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Description
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-----------
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The wakeup in preemptive (wip) monitor is a sample per-cpu monitor
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that verifies if the wakeup events always take place with
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preemption disabled::
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v
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#==================#
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H preemptive H <+
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#==================# |
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| preempt_disable | preempt_enable
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v |
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sched_waking +------------------+ |
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+--------------- | | |
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| | non_preemptive | |
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+--------------> | | -+
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+------------------+
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The wakeup event always takes place with preemption disabled because
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of the scheduler synchronization. However, because the preempt_count
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and its trace event are not atomic with regard to interrupts, some
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inconsistencies might happen. For example::
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preempt_disable() {
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__preempt_count_add(1)
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-------> smp_apic_timer_interrupt() {
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preempt_disable()
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do not trace (preempt count >= 1)
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wake up a thread
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preempt_enable()
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do not trace (preempt count >= 1)
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}
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<------
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trace_preempt_disable();
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}
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This problem was reported and discussed here:
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https://lore.kernel.org/r/cover.1559051152.git.bristot@redhat.com/
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Specification
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-------------
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Grapviz Dot file in tools/verification/models/wip.dot
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