758 lines
24 KiB
C
758 lines
24 KiB
C
/****************************************************************************
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* sched/irq/irq_csection.c
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*
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* Licensed to the Apache Software Foundation (ASF) under one or more
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* contributor license agreements. See the NOTICE file distributed with
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* this work for additional information regarding copyright ownership. The
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* ASF licenses this file to you under the Apache License, Version 2.0 (the
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* "License"); you may not use this file except in compliance with the
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* License. You may obtain a copy of the License at
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*
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* http://www.apache.org/licenses/LICENSE-2.0
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*
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* Unless required by applicable law or agreed to in writing, software
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* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
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* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
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* License for the specific language governing permissions and limitations
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* under the License.
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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 <assert.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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#ifdef CONFIG_IRQCOUNT
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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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/* Handles nested calls to enter_critical section from interrupt handlers */
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volatile 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_cpu_irqlock, handling a known deadlock condition:
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*
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* A deadlock may occur if enter_critical_section is called from an
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* interrupt handler. Suppose:
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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 same deadlock can occur in the normal tasking case:
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*
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* - A task on CPUn enters a critical section and has the g_cpu_irqlock
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* spinlock.
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* - Another task on CPUm attempts to enter the critical section but has
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* to wait, spinning to get g_cpu_irqlock with interrupts disabled.
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* - The task on CPUn causes a new task to become ready-to-run and the
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* scheduler selects CPUm. CPUm is requested to pause via a pause
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* interrupt.
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* - But the task on CPUm is also attempting to enter the critical
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* section. Since it is spinning with interrupts disabled, CPUm cannot
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* process the pending pause interrupt, causing the deadlock.
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*
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* This function detects this deadlock condition while spinning with
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* interrupts disabled.
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*
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* Input Parameters:
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* cpu - The index of CPU that is trying to enter the critical section.
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*
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* Returned Value:
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* True: The g_cpu_irqlock spinlock has been taken.
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* False: The g_cpu_irqlock spinlock has not been taken yet, but there is
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* a pending pause interrupt request.
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*
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****************************************************************************/
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#ifdef CONFIG_SMP
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static bool irq_waitlock(int cpu)
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{
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#ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS
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FAR struct tcb_s *tcb = current_task(cpu);
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/* Notify that we are waiting for a spinlock */
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sched_note_spinlock(tcb, &g_cpu_irqlock);
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#endif
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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 (spin_trylock_wo_note(&g_cpu_irqlock) == SP_LOCKED)
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{
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/* Is a pause request pending? */
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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!
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* Abort the wait and return false.
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*/
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#ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS
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/* Notify that we have aborted the wait for the spinlock */
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sched_note_spinabort(tcb, &g_cpu_irqlock);
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#endif
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return false;
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}
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}
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/* We have g_cpu_irqlock! */
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#ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS
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/* Notify that we have the spinlock */
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sched_note_spinlocked(tcb, &g_cpu_irqlock);
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#endif
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return true;
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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 incremented 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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try_again:
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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_nx_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 should 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 should 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_irqset 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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try_again_in_irq:
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if (!irq_waitlock(cpu))
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{
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/* We are in a deadlock condition due to a pending
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* pause request interrupt. Break the deadlock by
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* handling the pause request now.
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*/
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DEBUGVERIFY(up_cpu_paused(cpu));
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/* NOTE: As the result of up_cpu_paused(cpu), this CPU
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* might set g_cpu_irqset in nxsched_resume_scheduler()
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* However, another CPU might hold g_cpu_irqlock.
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* To avoid this situation, releae g_cpu_irqlock first.
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*/
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if ((g_cpu_irqset & (1 << cpu)) != 0)
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{
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spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
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&g_cpu_irqlock);
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}
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/* NOTE: Here, this CPU does not hold g_cpu_irqlock,
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* so call irq_waitlock(cpu) to acquire g_cpu_irqlock.
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*/
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goto try_again_in_irq;
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}
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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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/* Also set the CPU bit so that other CPUs will be aware that
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* this CPU holds the critical section.
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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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}
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}
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else
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{
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/* Normal tasking environment.
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*
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* Get the TCB of the currently executing task on this CPU (avoid
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* using this_task() which can recurse.
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*/
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cpu = this_cpu();
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rtcb = current_task(cpu);
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DEBUGASSERT(rtcb != NULL);
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/* Do we already have interrupts disabled? */
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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,
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* and (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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DEBUGASSERT((g_cpu_irqset & (1 << cpu)) == 0);
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if (!irq_waitlock(cpu))
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{
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/* We are in a deadlock condition due to a pending pause
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* request interrupt. Re-enable interrupts on this CPU
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* and try again. Briefly re-enabling interrupts should
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* be sufficient to permit processing the pending pause
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* request.
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*/
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up_irq_restore(ret);
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goto try_again;
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}
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/* Then 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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/* Note that we have entered the critical section */
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#ifdef CONFIG_SCHED_CRITMONITOR
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nxsched_critmon_csection(rtcb, true);
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#endif
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#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
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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
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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_nx_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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/* Have we just entered the critical section? Or is this a nested
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* call to enter_critical_section.
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*/
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DEBUGASSERT(rtcb->irqcount >= 0 && rtcb->irqcount < INT16_MAX);
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if (++rtcb->irqcount == 1)
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{
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/* Note that we have entered the critical section */
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#ifdef CONFIG_SCHED_CRITMONITOR
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nxsched_critmon_csection(rtcb, true);
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#endif
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#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
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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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/* 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_nx_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. Restore the g_cpu_irqset for this CPU
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* and release the spinlock (if necessary).
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*/
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DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
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g_cpu_nestcount[cpu] == 1);
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FAR struct tcb_s *rtcb = current_task(cpu);
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DEBUGASSERT(rtcb != NULL);
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if (rtcb->irqcount <= 0)
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{
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spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
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&g_cpu_irqlock);
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}
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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;
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/* Get the TCB of the currently executing task on this CPU (avoid
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* using this_task() which can recurse.
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*/
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cpu = this_cpu();
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rtcb = current_task(cpu);
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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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/* No.. Note that we have left the critical section */
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#ifdef CONFIG_SCHED_CRITMONITOR
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nxsched_critmon_csection(rtcb, false);
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#endif
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#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
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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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DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
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(g_cpu_irqset & (1 << cpu)) != 0);
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/* Check if releasing the lock held by this CPU will unlock the
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* critical section.
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*/
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if ((g_cpu_irqset & ~(1 << cpu)) == 0)
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{
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/* Yes.. Check if there are pending tasks and that pre-
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* emption is also enabled. This is necessary because we
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* may have deferred the up_release_pending() call in
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* sched_unlock() because we were within a critical
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* section then.
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*/
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if (g_pendingtasks.head != NULL &&
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!nxsched_islocked_global())
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{
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/* Release any ready-to-run tasks that have collected
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* in g_pendingtasks. NOTE: This operation has a very
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* high likelihood of causing this task to be switched
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* out!
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*/
|
|
|
|
up_release_pending();
|
|
}
|
|
}
|
|
|
|
/* Now, possibly on return from a context switch, clear our
|
|
* count on the lock. If all CPUs have released the lock,
|
|
* then unlock the global IRQ spinlock.
|
|
*/
|
|
|
|
rtcb->irqcount = 0;
|
|
spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
|
|
&g_cpu_irqlock);
|
|
|
|
/* Have all CPUs released the lock? */
|
|
}
|
|
}
|
|
}
|
|
|
|
/* Restore the previous interrupt state which may still be interrupts
|
|
* disabled (but we don't have a mechanism to verify that now)
|
|
*/
|
|
|
|
up_irq_restore(flags);
|
|
}
|
|
|
|
#else
|
|
|
|
void leave_critical_section(irqstate_t flags)
|
|
{
|
|
/* Check if we were called from an interrupt handler and that the tasks
|
|
* lists have been initialized.
|
|
*/
|
|
|
|
if (!up_interrupt_context() && g_nx_initstate >= OSINIT_TASKLISTS)
|
|
{
|
|
FAR struct tcb_s *rtcb = this_task();
|
|
DEBUGASSERT(rtcb != NULL);
|
|
|
|
/* Have we left entered the critical section? Or are we still
|
|
* nested.
|
|
*/
|
|
|
|
DEBUGASSERT(rtcb->irqcount > 0);
|
|
if (--rtcb->irqcount <= 0)
|
|
{
|
|
/* Note that we have left the critical section */
|
|
|
|
#ifdef CONFIG_SCHED_CRITMONITOR
|
|
nxsched_critmon_csection(rtcb, false);
|
|
#endif
|
|
#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
|
|
sched_note_csection(rtcb, false);
|
|
#endif
|
|
}
|
|
}
|
|
|
|
/* Restore the previous interrupt state. */
|
|
|
|
up_irq_restore(flags);
|
|
}
|
|
#endif
|
|
|
|
/****************************************************************************
|
|
* Name: irq_cpu_locked
|
|
*
|
|
* Description:
|
|
* Test if the IRQ lock set OR if this CPU holds the IRQ lock
|
|
* There is an interaction with pre-emption controls and IRQ locking:
|
|
* Even if the pre-emption is enabled, tasks will be forced to pend if
|
|
* the IRQ lock is also set UNLESS the CPU starting the task is the
|
|
* holder of the IRQ lock.
|
|
*
|
|
* Input Parameters:
|
|
* cpu - Points to which cpu
|
|
*
|
|
* Returned Value:
|
|
* true - IRQs are locked by a different CPU.
|
|
* false - IRQs are unlocked OR if they are locked BUT this CPU
|
|
* is the holder of the lock.
|
|
*
|
|
* Warning: This values are volatile at only valid at the instance that
|
|
* the CPU set was queried.
|
|
*
|
|
****************************************************************************/
|
|
|
|
#ifdef CONFIG_SMP
|
|
bool irq_cpu_locked(int cpu)
|
|
{
|
|
cpu_set_t irqset;
|
|
|
|
/* g_cpu_irqset is not valid in early phases of initialization */
|
|
|
|
if (g_nx_initstate < OSINIT_OSREADY)
|
|
{
|
|
/* We are still single threaded. In either state of g_cpu_irqlock,
|
|
* the correct return value should always be false.
|
|
*/
|
|
|
|
return false;
|
|
}
|
|
|
|
/* Test if g_cpu_irqlock is locked. We don't really need to use check
|
|
* g_cpu_irqlock to do this, we can use the g_cpu_set.
|
|
*
|
|
* Sample the g_cpu_irqset once. That is an atomic operation. All
|
|
* subsequent operations will operate on the sampled cpu set.
|
|
*/
|
|
|
|
irqset = (cpu_set_t)g_cpu_irqset;
|
|
if (irqset != 0)
|
|
{
|
|
/* Some CPU holds the lock. So g_cpu_irqlock should be locked.
|
|
* Return false if the 'cpu' is the holder of the lock; return
|
|
* true if g_cpu_irqlock is locked, but this CPU is not the
|
|
* holder of the lock.
|
|
*/
|
|
|
|
return ((irqset & (1 << cpu)) == 0);
|
|
}
|
|
|
|
/* No CPU holds the lock */
|
|
|
|
else
|
|
{
|
|
/* In this case g_cpu_irqlock should be unlocked. However, if
|
|
* the lock was established in the interrupt handler AND there are
|
|
* no bits set in g_cpu_irqset, that probably means only that
|
|
* critical section was established from an interrupt handler.
|
|
* Return false in either case.
|
|
*/
|
|
|
|
return false;
|
|
}
|
|
}
|
|
#endif
|
|
|
|
/****************************************************************************
|
|
* Name: restore_critical_section
|
|
*
|
|
* Description:
|
|
* Restore the critical_section
|
|
*
|
|
* Input Parameters:
|
|
* None
|
|
*
|
|
* Returned Value:
|
|
* None
|
|
*
|
|
****************************************************************************/
|
|
|
|
#ifdef CONFIG_SMP
|
|
void restore_critical_section(void)
|
|
{
|
|
/* NOTE: The following logic for adjusting global IRQ controls were
|
|
* derived from nxsched_add_readytorun() and sched_removedreadytorun()
|
|
* Here, we only handles clearing logic to defer unlocking IRQ lock
|
|
* followed by context switching.
|
|
*/
|
|
|
|
FAR struct tcb_s *tcb = this_task();
|
|
int me = this_cpu();
|
|
|
|
/* Adjust global IRQ controls. If irqcount is greater than zero,
|
|
* then this task/this CPU holds the IRQ lock
|
|
*/
|
|
|
|
if (tcb->irqcount > 0)
|
|
{
|
|
/* Do notihing here
|
|
* NOTE: spin_setbit() is done in nxsched_add_readytorun()
|
|
* and nxsched_remove_readytorun()
|
|
*/
|
|
}
|
|
|
|
/* No.. This CPU will be relinquishing the lock. But this works
|
|
* differently if we are performing a context switch from an
|
|
* interrupt handler and the interrupt handler has established
|
|
* a critical section. We can detect this case when
|
|
* g_cpu_nestcount[me] > 0.
|
|
*/
|
|
|
|
else if (g_cpu_nestcount[me] <= 0)
|
|
{
|
|
/* Release our hold on the IRQ lock. */
|
|
|
|
if ((g_cpu_irqset & (1 << me)) != 0)
|
|
{
|
|
spin_clrbit(&g_cpu_irqset, me, &g_cpu_irqsetlock,
|
|
&g_cpu_irqlock);
|
|
}
|
|
}
|
|
}
|
|
#endif /* CONFIG_SMP */
|
|
|
|
#endif /* CONFIG_IRQCOUNT */
|