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incubator-nuttx/sched/irq/irq_csection.c

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/****************************************************************************
* sched/irq/irq_csection.c
*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership. The
* ASF licenses this file to you under the Apache License, Version 2.0 (the
* "License"); you may not use this file except in compliance with the
* License. You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
* WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
* License for the specific language governing permissions and limitations
* under the License.
*
****************************************************************************/
/****************************************************************************
* Included Files
****************************************************************************/
#include <nuttx/config.h>
#include <sys/types.h>
#include <assert.h>
#include <nuttx/init.h>
#include <nuttx/spinlock.h>
#include <nuttx/sched_note.h>
#include <arch/irq.h>
#include "sched/sched.h"
#include "irq/irq.h"
#ifdef CONFIG_IRQCOUNT
/****************************************************************************
* Public Data
****************************************************************************/
#ifdef CONFIG_SMP
/* This is the spinlock that enforces critical sections when interrupts are
* disabled.
*/
volatile spinlock_t g_cpu_irqlock = SP_UNLOCKED;
/* Used to keep track of which CPU(s) hold the IRQ lock. */
volatile spinlock_t g_cpu_irqsetlock;
volatile cpu_set_t g_cpu_irqset;
/* Handles nested calls to enter_critical section from interrupt handlers */
volatile uint8_t g_cpu_nestcount[CONFIG_SMP_NCPUS];
#endif
/****************************************************************************
* Private Functions
****************************************************************************/
/****************************************************************************
* Name: irq_waitlock
*
* Description:
* Spin to get g_cpu_irqlock, handling a known deadlock condition:
*
* A deadlock may occur if enter_critical_section is called from an
* interrupt handler. Suppose:
*
* - CPUn is in a critical section and has the g_cpu_irqlock spinlock.
* - CPUm takes an interrupt and attempts to enter the critical section.
* - It spins waiting on g_cpu_irqlock with interrupts disabled.
* - CPUn calls up_cpu_pause() to pause operation on CPUm. This will
* issue an inter-CPU interrupt to CPUm
* - But interrupts are disabled on CPUm so the up_cpu_pause() is never
* handled, causing the deadlock.
*
* This same deadlock can occur in the normal tasking case:
*
* - A task on CPUn enters a critical section and has the g_cpu_irqlock
* spinlock.
* - Another task on CPUm attempts to enter the critical section but has
* to wait, spinning to get g_cpu_irqlock with interrupts disabled.
* - The task on CPUn causes a new task to become ready-to-run and the
* scheduler selects CPUm. CPUm is requested to pause via a pause
* interrupt.
* - But the task on CPUm is also attempting to enter the critical
* section. Since it is spinning with interrupts disabled, CPUm cannot
* process the pending pause interrupt, causing the deadlock.
*
* This function detects this deadlock condition while spinning with
* interrupts disabled.
*
* Input Parameters:
* cpu - The index of CPU that is trying to enter the critical section.
*
* Returned Value:
* True: The g_cpu_irqlock spinlock has been taken.
* False: The g_cpu_irqlock spinlock has not been taken yet, but there is
* a pending pause interrupt request.
*
****************************************************************************/
#ifdef CONFIG_SMP
static bool irq_waitlock(int cpu)
{
#ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS
FAR struct tcb_s *tcb = current_task(cpu);
/* Notify that we are waiting for a spinlock */
sched_note_spinlock(tcb, &g_cpu_irqlock, NOTE_SPINLOCK_LOCK);
#endif
/* Duplicate the spin_lock() logic from spinlock.c, but adding the check
* for the deadlock condition.
*/
while (spin_trylock_wo_note(&g_cpu_irqlock) == SP_LOCKED)
{
/* Is a pause request pending? */
if (up_cpu_pausereq(cpu))
{
/* Yes.. some other CPU is requesting to pause this CPU!
* Abort the wait and return false.
*/
#ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS
/* Notify that we have aborted the wait for the spinlock */
sched_note_spinlock(tcb, &g_cpu_irqlock, NOTE_SPINLOCK_ABORT);
#endif
return false;
}
}
/* We have g_cpu_irqlock! */
#ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS
/* Notify that we have the spinlock */
sched_note_spinlock(tcb, &g_cpu_irqlock, NOTE_SPINLOCK_LOCKED);
#endif
return true;
}
#endif
/****************************************************************************
* Public Functions
****************************************************************************/
/****************************************************************************
* Name: enter_critical_section
*
* Description:
* Take the CPU IRQ lock and disable interrupts on all CPUs. A thread-
* specific counter is incremented to indicate that the thread has IRQs
* disabled and to support nested calls to enter_critical_section().
*
****************************************************************************/
#ifdef CONFIG_SMP
irqstate_t enter_critical_section(void)
{
FAR struct tcb_s *rtcb;
irqstate_t ret;
int cpu;
/* Disable interrupts.
*
* NOTE 1: Ideally this should disable interrupts on all CPUs, but most
* architectures only support disabling interrupts on the local CPU.
* NOTE 2: Interrupts may already be disabled, but we call up_irq_save()
* unconditionally because we need to return valid interrupt status in any
* event.
* NOTE 3: We disable local interrupts BEFORE taking the spinlock in order
* to prevent possible waits on the spinlock from interrupt handling on
* the local CPU.
*/
try_again:
ret = up_irq_save();
/* Verify that the system has sufficiently initialized so that the task
* lists are valid.
*/
if (g_nx_initstate >= OSINIT_TASKLISTS)
{
/* If called from an interrupt handler, then just take the spinlock.
* If we are already in a critical section, this will lock the CPU
* in the interrupt handler. Sounds worse than it is.
*/
if (up_interrupt_context())
{
/* We are in an interrupt handler. How can this happen?
*
* 1. We were not in a critical section when the interrupt
* occurred. In this case, the interrupt was entered with:
*
* g_cpu_irqlock = SP_UNLOCKED.
* g_cpu_nestcount = 0
* All CPU bits in g_cpu_irqset should be zero
*
* 2. We were in a critical section and interrupts on this
* this CPU were disabled -- this is an impossible case.
*
* 3. We were in critical section, but up_irq_save() only
* disabled local interrupts on a different CPU;
* Interrupts could still be enabled on this CPU.
*
* g_cpu_irqlock = SP_LOCKED.
* g_cpu_nestcount = 0
* The bit in g_cpu_irqset for this CPU should be zero
*
* 4. An extension of 3 is that we may be re-entered numerous
* times from the same interrupt handler. In that case:
*
* g_cpu_irqlock = SP_LOCKED.
* g_cpu_nestcount > 0
* The bit in g_cpu_irqset for this CPU should be zero
*
* NOTE: However, the interrupt entry conditions can change due
* to previous processing by the interrupt handler that may
* instantiate a new thread that has irqcount > 0 and may then
* set the bit in g_cpu_irqset and g_cpu_irqlock = SP_LOCKED
*/
/* Handle nested calls to enter_critical_section() from the same
* interrupt.
*/
cpu = this_cpu();
if (g_cpu_nestcount[cpu] > 0)
{
DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
g_cpu_nestcount[cpu] < UINT8_MAX);
g_cpu_nestcount[cpu]++;
}
/* This is the first call to enter_critical_section from the
* interrupt handler.
*/
else
{
/* Make sure that the g_cpu_irqset was not already set
* by previous logic on this CPU that was executed by the
* interrupt handler. We know that the bit in g_cpu_irqset
* for this CPU was zero on entry into the interrupt handler,
* so if it is non-zero now then we know that was the case.
*/
if ((g_cpu_irqset & (1 << cpu)) == 0)
{
/* Wait until we can get the spinlock (meaning that we are
* no longer blocked by the critical section).
*/
try_again_in_irq:
if (!irq_waitlock(cpu))
{
/* We are in a deadlock condition due to a pending
* pause request interrupt. Break the deadlock by
* handling the pause request now.
*/
DEBUGVERIFY(up_cpu_paused(cpu));
/* NOTE: As the result of up_cpu_paused(cpu), this CPU
* might set g_cpu_irqset in nxsched_resume_scheduler()
* However, another CPU might hold g_cpu_irqlock.
* To avoid this situation, releae g_cpu_irqlock first.
*/
if ((g_cpu_irqset & (1 << cpu)) != 0)
{
spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
&g_cpu_irqlock);
}
/* NOTE: Here, this CPU does not hold g_cpu_irqlock,
* so call irq_waitlock(cpu) to acquire g_cpu_irqlock.
*/
goto try_again_in_irq;
}
}
/* In any event, the nesting count is now one */
g_cpu_nestcount[cpu] = 1;
/* Also set the CPU bit so that other CPUs will be aware that
* this CPU holds the critical section.
*/
spin_setbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
&g_cpu_irqlock);
}
}
else
{
/* Normal tasking environment.
*
* Get the TCB of the currently executing task on this CPU (avoid
* using this_task() which can recurse.
*/
cpu = this_cpu();
rtcb = current_task(cpu);
DEBUGASSERT(rtcb != NULL);
/* Do we already have interrupts disabled? */
if (rtcb->irqcount > 0)
{
/* Yes... make sure that the spinlock is set and increment the
* IRQ lock count.
*
* NOTE: If irqcount > 0 then (1) we are in a critical section,
* and (2) this CPU should hold the lock.
*/
DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
(g_cpu_irqset & (1 << this_cpu())) != 0 &&
rtcb->irqcount < INT16_MAX);
rtcb->irqcount++;
}
else
{
/* If we get here with irqcount == 0, then we know that the
* current task running on this CPU is not in a critical
* section. However other tasks on other CPUs may be in a
* critical section. If so, we must wait until they release
* the spinlock.
*/
DEBUGASSERT((g_cpu_irqset & (1 << cpu)) == 0);
if (!irq_waitlock(cpu))
{
/* We are in a deadlock condition due to a pending pause
* request interrupt. Re-enable interrupts on this CPU
* and try again. Briefly re-enabling interrupts should
* be sufficient to permit processing the pending pause
* request.
*/
up_irq_restore(ret);
goto try_again;
}
/* Then set the lock count to 1.
*
* Interrupts disables must follow a stacked order. We
* cannot other context switches to re-order the enabling
* disabling of interrupts.
*
* The scheduler accomplishes this by treating the irqcount
* like lockcount: Both will disable pre-emption.
*/
spin_setbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
&g_cpu_irqlock);
rtcb->irqcount = 1;
/* Note that we have entered the critical section */
#ifdef CONFIG_SCHED_CRITMONITOR
nxsched_critmon_csection(rtcb, true);
#endif
#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
sched_note_csection(rtcb, true);
#endif
}
}
}
/* Return interrupt status */
return ret;
}
#else
irqstate_t enter_critical_section(void)
{
irqstate_t ret;
/* Disable interrupts */
ret = up_irq_save();
/* Check if we were called from an interrupt handler and that the task
* 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 just entered the critical section? Or is this a nested
* call to enter_critical_section.
*/
DEBUGASSERT(rtcb->irqcount >= 0 && rtcb->irqcount < INT16_MAX);
if (++rtcb->irqcount == 1)
{
/* Note that we have entered the critical section */
#ifdef CONFIG_SCHED_CRITMONITOR
nxsched_critmon_csection(rtcb, true);
#endif
#ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION
sched_note_csection(rtcb, true);
#endif
}
}
/* Return interrupt status */
return ret;
}
#endif
/****************************************************************************
* Name: leave_critical_section
*
* Description:
* Decrement the IRQ lock count and if it decrements to zero then release
* the spinlock.
*
****************************************************************************/
#ifdef CONFIG_SMP
void leave_critical_section(irqstate_t flags)
{
int cpu;
/* Verify that the system has sufficiently initialized so that the task
* lists are valid.
*/
if (g_nx_initstate >= OSINIT_TASKLISTS)
{
/* If called from an interrupt handler, then just release the
* spinlock. The interrupt handling logic should already hold the
* spinlock if enter_critical_section() has been called. Unlocking
* the spinlock will allow interrupt handlers on other CPUs to execute
* again.
*/
if (up_interrupt_context())
{
/* We are in an interrupt handler. Check if the last call to
* enter_critical_section() was nested.
*/
cpu = this_cpu();
if (g_cpu_nestcount[cpu] > 1)
{
/* Yes.. then just decrement the nesting count */
DEBUGASSERT(spin_islocked(&g_cpu_irqlock));
g_cpu_nestcount[cpu]--;
}
else
{
/* No, not nested. Restore the g_cpu_irqset for this CPU
* and release the spinlock (if necessary).
*/
DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
g_cpu_nestcount[cpu] == 1);
FAR struct tcb_s *rtcb = current_task(cpu);
DEBUGASSERT(rtcb != NULL);
if (rtcb->irqcount <= 0)
{
spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock,
&g_cpu_irqlock);
}
g_cpu_nestcount[cpu] = 0;
}
}
else
{
FAR struct tcb_s *rtcb;
/* Get the TCB of the currently executing task on this CPU (avoid
* using this_task() which can recurse.
*/
cpu = this_cpu();
rtcb = current_task(cpu);
DEBUGASSERT(rtcb != NULL && rtcb->irqcount > 0);
/* Normal tasking context. We need to coordinate with other
* tasks.
*
* Will we still have interrupts disabled after decrementing the
* count?
*/
if (rtcb->irqcount > 1)
{
/* Yes... the spinlock should remain set */
DEBUGASSERT(spin_islocked(&g_cpu_irqlock));
rtcb->irqcount--;
}
else
{
/* No.. 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
/* Decrement our count on the lock. If all CPUs have
* released, then unlock the spinlock.
*/
DEBUGASSERT(spin_islocked(&g_cpu_irqlock) &&
(g_cpu_irqset & (1 << cpu)) != 0);
/* Check if releasing the lock held by this CPU will unlock the
* critical section.
*/
if ((g_cpu_irqset & ~(1 << cpu)) == 0)
{
/* Yes.. Check if there are pending tasks and that pre-
* emption is also enabled. This is necessary because we
* may have deferred the nxsched_merge_pending() call in
* sched_unlock() because we were within a critical
* section then.
*/
if (g_pendingtasks.head != NULL &&
!nxsched_islocked_global())
{
/* Release any ready-to-run tasks that have collected
* in g_pendingtasks. NOTE: This operation has a very
* high likelihood of causing this task to be switched
* out!
*/
if (nxsched_merge_pending())
{
up_switch_context(this_task(), rtcb);
}
}
}
/* 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 */
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