525 lines
18 KiB
C
525 lines
18 KiB
C
/****************************************************************************
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* sched/irq/irq_csection.c
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*
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* Copyright (C) 2016 Gregory Nutt. All rights reserved.
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* Author: Gregory Nutt <gnutt@nuttx.org>
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*
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* Redistribution and use in source and binary forms, with or without
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* modification, are permitted provided that the following conditions
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* are met:
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*
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* 1. Redistributions of source code must retain the above copyright
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* notice, this list of conditions and the following disclaimer.
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* 2. Redistributions in binary form must reproduce the above copyright
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* notice, this list of conditions and the following disclaimer in
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* the documentation and/or other materials provided with the
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* distribution.
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* 3. Neither the name NuttX nor the names of its contributors may be
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* used to endorse or promote products derived from this software
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* without specific prior written permission.
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*
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* THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS
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* "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT
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* LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS
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* FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE
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* COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT,
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* INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING,
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* BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS
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* OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED
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* AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT
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* LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN
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* ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE
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* POSSIBILITY OF SUCH DAMAGE.
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*
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****************************************************************************/
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/****************************************************************************
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* Included Files
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****************************************************************************/
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#include <nuttx/config.h>
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#include <sys/types.h>
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#include <nuttx/init.h>
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#include <nuttx/spinlock.h>
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#include <nuttx/sched_note.h>
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#include <arch/irq.h>
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#include "sched/sched.h"
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#include "irq/irq.h"
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#if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION)
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/****************************************************************************
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* Public Data
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****************************************************************************/
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#ifdef CONFIG_SMP
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/* This is the spinlock that enforces critical sections when interrupts are
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* disabled.
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*/
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volatile spinlock_t g_cpu_irqlock = SP_UNLOCKED;
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/* Used to keep track of which CPU(s) hold the IRQ lock. */
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volatile spinlock_t g_cpu_irqsetlock;
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volatile cpu_set_t g_cpu_irqset;
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#endif
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/****************************************************************************
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* Private Data
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****************************************************************************/
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#ifdef CONFIG_SMP
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/* Handles nested calls to enter_critical section from interrupt handlers */
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static uint8_t g_cpu_nestcount[CONFIG_SMP_NCPUS];
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#endif
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/****************************************************************************
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* Private Functions
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****************************************************************************/
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/****************************************************************************
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* Name: irq_waitlock
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*
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* Description:
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* Spin to get g_irq_waitlock, handling a known deadlock condition:
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*
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* Suppose this situation:
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*
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* - CPUn is in a critical section and has the g_cpu_irqlock spinlock.
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* - CPUm takes an interrupt and attempts to enter the critical section.
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* - It spins waiting on g_cpu_irqlock with interrupts disabled.
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* - CPUn calls up_cpu_pause() to pause operation on CPUm. This will
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* issue an inter-CPU interrupt to CPUm
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* - But interrupts are disabled on CPUm so the up_cpu_pause() is never
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* handled, causing the deadlock.
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*
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* This function detects this deadlock condition while spinning in an
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* interrupt and calls up_cpu_pause() handler, breaking the deadlock.
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*
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****************************************************************************/
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#ifdef CONFIG_SMP
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static inline void irq_waitlock(int cpu)
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{
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/* Duplicate the spin_lock() logic from spinlock.c, but adding the check
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* for the deadlock condition.
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*/
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while (up_testset(&g_cpu_irqlock) == SP_LOCKED)
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{
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/* A deadlock condition would occur if CPUn:
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*
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* 1. Holds the g_cpu_irqlock, and
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* 2. Is trying to interrupt CPUm, but
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* 3. CPUm is spinning trying acquaire the g_cpu_irqlock.
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*
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* The protocol for CPUn to pause CPUm is as follows
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*
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* 1. The up_cpu_pause() implementation on CPUn locks both
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* g_cpu_wait[m] and g_cpu_paused[m]. CPUn then waits
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* spinning on g_cpu_wait[m].
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* 2. When CPUm receives the interrupt it (1) unlocks
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* g_cpu_paused[m] and (2) locks g_cpu_wait[m]. The
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* first unblocks CPUn and the second blocks CPUm in the
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* interrupt handler.
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*
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* The problem in the deadlock case is that CPUm cannot receive
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* the interrupt because it is locked up spinning. Here we break
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* the deadlock here be handling the pause interrupt request
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* while waiting.
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*/
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if (up_cpu_pausereq(cpu))
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{
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/* Yes.. some other CPU is requesting to pause this CPU! Handle
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* the pause interrupt now.
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*/
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DEBUGVERIFY(up_cpu_paused(cpu));
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}
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SP_DSB();
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}
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/* We have g_cpu_irqlock! */
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SP_DMB();
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}
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#endif
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/****************************************************************************
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* Public Functions
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****************************************************************************/
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/****************************************************************************
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* Name: enter_critical_section
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*
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* Description:
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* Take the CPU IRQ lock and disable interrupts on all CPUs. A thread-
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* specific counter is increment to indicate that the thread has IRQs
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* disabled and to support nested calls to enter_critical_section().
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*
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****************************************************************************/
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#ifdef CONFIG_SMP
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irqstate_t enter_critical_section(void)
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{
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FAR struct tcb_s *rtcb;
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irqstate_t ret;
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int cpu;
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/* Disable interrupts.
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*
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* NOTE 1: Ideally this should disable interrupts on all CPUs, but most
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* architectures only support disabling interrupts on the local CPU.
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* NOTE 2: Interrupts may already be disabled, but we call up_irq_save()
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* unconditionally because we need to return valid interrupt status in any
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* event.
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* NOTE 3: We disable local interrupts BEFORE taking the spinlock in order
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* to prevent possible waits on the spinlock from interrupt handling on
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* the local CPU.
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*/
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ret = up_irq_save();
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/* Verify that the system has sufficiently initialized so that the task
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* lists are valid.
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*/
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if (g_os_initstate >= OSINIT_TASKLISTS)
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{
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/* If called from an interrupt handler, then just take the spinlock.
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* If we are already in a critical section, this will lock the CPU
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* in the interrupt handler. Sounds worse than it is.
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*/
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if (up_interrupt_context())
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{
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/* We are in an interrupt handler. How can this happen?
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*
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* 1. We were not in a critical section when the interrupt
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* occurred. In this case, the interrupt was entered with:
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*
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* g_cpu_irqlock = SP_UNLOCKED.
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* g_cpu_nestcount = 0
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* All CPU bits in g_cpu_irqset should be zero
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*
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* 2. We were in a critical section and interrupts on this
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* this CPU were disabled -- this is an impossible case.
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*
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* 3. We were in critical section, but up_irq_save() only
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* disabled local interrupts on a different CPU;
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* Interrupts could still be enabled on this CPU.
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*
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* g_cpu_irqlock = SP_LOCKED.
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* g_cpu_nestcount = 0
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* The bit in g_cpu_irqset for this CPU hould be zero
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*
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* 4. An extension of 3 is that we may be re-entered numerous
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* times from the same interrupt handler. In that case:
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*
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* g_cpu_irqlock = SP_LOCKED.
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* g_cpu_nestcount > 0
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* The bit in g_cpu_irqset for this CPU hould be zero
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*
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* NOTE: However, the interrupt entry conditions can change due
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* to previous processing by the interrupt handler that may
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* instantiate a new thread that has irqcount > 0 and may then
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* set the bit in g_cpu_irqset and g_cpu_irqlock = SP_LOCKED
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*/
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/* Handle nested calls to enter_critical_section() from the same
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* interrupt.
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*/
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cpu = this_cpu();
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if (g_cpu_nestcount[cpu] > 0)
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{
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DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
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g_cpu_nestcount[cpu] < UINT8_MAX);
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g_cpu_nestcount[cpu]++;
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}
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/* This is the first call to enter_critical_section from the
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* interrupt handler.
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*/
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else
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{
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/* Make sure that the g_cpu_irqlock() was not already set
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* by previous logic on this CPU that was executed by the
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* interrupt handler. We know that the bit in g_cpu_irqset
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* for this CPU was zero on entry into the interrupt handler,
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* so if it is non-zero now then we know that was the case.
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*/
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if ((g_cpu_irqset & (1 << cpu)) == 0)
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{
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/* Wait until we can get the spinlock (meaning that we are
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* no longer blocked by the critical section).
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*/
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irq_waitlock(cpu);
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}
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/* In any event, the nesting count is now one */
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g_cpu_nestcount[cpu] = 1;
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}
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}
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else
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{
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/* Normal tasking environment. */
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/* Do we already have interrupts disabled? */
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rtcb = this_task();
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DEBUGASSERT(rtcb != NULL);
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if (rtcb->irqcount > 0)
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{
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/* Yes... make sure that the spinlock is set and increment the
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* IRQ lock count.
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*
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* NOTE: If irqcount > 0 then (1) we are in a critical section, and
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* (2) this CPU should hold the lock.
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*/
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DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
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(g_cpu_irqset & (1 << this_cpu())) != 0 &&
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rtcb->irqcount < INT16_MAX);
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rtcb->irqcount++;
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}
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else
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{
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/* If we get here with irqcount == 0, then we know that the
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* current task running on this CPU is not in a critical
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* section. However other tasks on other CPUs may be in a
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* critical section. If so, we must wait until they release
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* the spinlock.
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*/
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cpu = this_cpu();
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DEBUGASSERT((g_cpu_irqset & (1 << cpu)) == 0);
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spin_lock(&g_cpu_irqlock);
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/* The set the lock count to 1.
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*
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* Interrupts disables must follow a stacked order. We
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* cannot other context switches to re-order the enabling
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* disabling of interrupts.
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*
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* The scheduler accomplishes this by treating the irqcount
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* like lockcount: Both will disable pre-emption.
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*/
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spin_setbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
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&g_cpu_irqlock);
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rtcb->irqcount = 1;
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#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
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/* Note that we have entered the critical section */
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sched_note_csection(rtcb, true);
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#endif
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}
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}
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}
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/* Return interrupt status */
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return ret;
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}
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#else /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) */
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irqstate_t enter_critical_section(void)
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{
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irqstate_t ret;
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/* Disable interrupts */
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ret = up_irq_save();
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/* Check if we were called from an interrupt handler and that the task
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* lists have been initialized.
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*/
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if (!up_interrupt_context() && g_os_initstate >= OSINIT_TASKLISTS)
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{
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FAR struct tcb_s *rtcb = this_task();
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DEBUGASSERT(rtcb != NULL);
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/* Yes.. Note that we have entered the critical section */
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sched_note_csection(rtcb, true);
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}
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/* Return interrupt status */
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return ret;
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}
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#endif
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/****************************************************************************
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* Name: leave_critical_section
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*
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* Description:
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* Decrement the IRQ lock count and if it decrements to zero then release
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* the spinlock.
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*
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****************************************************************************/
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#ifdef CONFIG_SMP
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void leave_critical_section(irqstate_t flags)
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{
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int cpu;
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/* Verify that the system has sufficiently initialized so that the task
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* lists are valid.
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*/
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if (g_os_initstate >= OSINIT_TASKLISTS)
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{
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/* If called from an interrupt handler, then just release the
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* spinlock. The interrupt handling logic should already hold the
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* spinlock if enter_critical_section() has been called. Unlocking
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* the spinlock will allow interrupt handlers on other CPUs to execute
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* again.
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*/
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if (up_interrupt_context())
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{
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/* We are in an interrupt handler. Check if the last call to
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* enter_critical_section() was nested.
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*/
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cpu = this_cpu();
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if (g_cpu_nestcount[cpu] > 1)
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{
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/* Yes.. then just decrement the nesting count */
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DEBUGASSERT(spin_islocked(&g_cpu_irqlock));
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g_cpu_nestcount[cpu]--;
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}
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else
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{
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/* No, not nested. Release the spinlock. */
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DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
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g_cpu_nestcount[cpu] == 1);
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spin_lock(&g_cpu_irqsetlock); /* Protects g_cpu_irqset */
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if (g_cpu_irqset == 0)
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{
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spin_unlock(&g_cpu_irqlock);
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}
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spin_unlock(&g_cpu_irqsetlock);
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g_cpu_nestcount[cpu] = 0;
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}
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}
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else
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{
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FAR struct tcb_s *rtcb = this_task();
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DEBUGASSERT(rtcb != NULL && rtcb->irqcount > 0);
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/* Normal tasking context. We need to coordinate with other
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* tasks.
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*
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* Will we still have interrupts disabled after decrementing the
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* count?
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*/
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if (rtcb->irqcount > 1)
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{
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/* Yes... the spinlock should remain set */
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DEBUGASSERT(spin_islocked(&g_cpu_irqlock));
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rtcb->irqcount--;
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}
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else
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{
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#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
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/* No.. Note that we have left the critical section */
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sched_note_csection(rtcb, false);
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#endif
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/* Decrement our count on the lock. If all CPUs have
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* released, then unlock the spinlock.
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*/
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cpu = this_cpu();
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DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
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(g_cpu_irqset & (1 << cpu)) != 0);
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rtcb->irqcount = 0;
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spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
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&g_cpu_irqlock);
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/* Have all CPUs released the lock? */
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if (!spin_islocked(&g_cpu_irqlock))
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{
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/* Check if there are pending tasks and that pre-emption
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* is also enabled.
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*
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* REVISIT: Is there an issue here? up_release_pending()
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* must be called from within a critical section but here
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* we have just left the critical section. At least we
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* still have interrupts disabled on this CPU.
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*/
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if (g_pendingtasks.head != NULL &&
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!spin_islocked(&g_cpu_schedlock))
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{
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/* Release any ready-to-run tasks that have collected
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* in g_pendingtasks if the scheduler is not locked.
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*
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* NOTE: This operation has a very high likelihood of
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* causing this task to be switched out!
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*
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* REVISIT: Should this not be done while we are in the
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* critical section.
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*/
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up_release_pending();
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}
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}
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}
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}
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}
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/* Restore the previous interrupt state which may still be interrupts
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* disabled (but we don't have a mechanism to verify that now)
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*/
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up_irq_restore(flags);
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}
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#else /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) */
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void leave_critical_section(irqstate_t flags)
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{
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/* Check if we were called from an interrupt handler and that the tasks
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* lists have been initialized.
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*/
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if (!up_interrupt_context() && g_os_initstate >= OSINIT_TASKLISTS)
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{
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FAR struct tcb_s *rtcb = this_task();
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DEBUGASSERT(rtcb != NULL);
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/* Yes.. Note that we have left the critical section */
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sched_note_csection(rtcb, false);
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}
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/* Restore the previous interrupt state. */
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up_irq_restore(flags);
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}
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#endif
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#endif /* CONFIG_SMP || CONFIG_SCHED_INSTRUMENTATION_CSECTION*/
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