/**************************************************************************** * 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 #include #include #include #include #include #include #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); #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_spinabort(tcb, &g_cpu_irqlock); #endif return false; } } /* We have g_cpu_irqlock! */ #ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS /* Notify that we have the spinlock */ sched_note_spinlocked(tcb, &g_cpu_irqlock); #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 up_release_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! */ 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: * rtcb - Points to the blocked TCB that is ready-to-run * * 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 #endif /* CONFIG_IRQCOUNT */