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The wakeup in preemptive (wip) monitor verifies if the
wakeup events always take place with preemption disabled:
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v
#==================#
H preemptive H <+
#==================# |
| |
| preempt_disable | preempt_enable
v |
sched_waking +------------------+ |
+--------------- | | |
| | non_preemptive | |
+--------------> | | -+
+------------------+
The wakeup event always takes place with preemption disabled because
of the scheduler synchronization. However, because the preempt_count
and its trace event are not atomic with regard to interrupts, some
inconsistencies might happen.
The documentation illustrates one of these cases.
Link: https://lkml.kernel.org/r/c98ca678df81115fddc04921b3c79720c836b18f.1659052063.git.bristot@kernel.org
Cc: Wim Van Sebroeck <wim@linux-watchdog.org>
Cc: Guenter Roeck <linux@roeck-us.net>
Cc: Jonathan Corbet <corbet@lwn.net>
Cc: Ingo Molnar <mingo@redhat.com>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Will Deacon <will@kernel.org>
Cc: Catalin Marinas <catalin.marinas@arm.com>
Cc: Marco Elver <elver@google.com>
Cc: Dmitry Vyukov <dvyukov@google.com>
Cc: "Paul E. McKenney" <paulmck@kernel.org>
Cc: Shuah Khan <skhan@linuxfoundation.org>
Cc: Gabriele Paoloni <gpaoloni@redhat.com>
Cc: Juri Lelli <juri.lelli@redhat.com>
Cc: Clark Williams <williams@redhat.com>
Cc: Tao Zhou <tao.zhou@linux.dev>
Cc: Randy Dunlap <rdunlap@infradead.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Cc: linux-trace-devel@vger.kernel.org
Signed-off-by: Daniel Bristot de Oliveira <bristot@kernel.org>
Signed-off-by: Steven Rostedt (Google) <rostedt@goodmis.org>
56 lines
1.6 KiB
ReStructuredText
56 lines
1.6 KiB
ReStructuredText
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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| |
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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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