/**************************************************************************** * sched/irq/irq_csection.c * * Copyright (C) 2016 Gregory Nutt. All rights reserved. * Author: Gregory Nutt * * Redistribution and use in source and binary forms, with or without * modification, are permitted provided that the following conditions * are met: * * 1. Redistributions of source code must retain the above copyright * notice, this list of conditions and the following disclaimer. * 2. Redistributions in binary form must reproduce the above copyright * notice, this list of conditions and the following disclaimer in * the documentation and/or other materials provided with the * distribution. * 3. Neither the name NuttX nor the names of its contributors may be * used to endorse or promote products derived from this software * without specific prior written permission. * * THIS SOFTWARE IS PROVIDED BY THE COPYRIGHT HOLDERS AND CONTRIBUTORS * "AS IS" AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT * LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS * FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL THE * COPYRIGHT OWNER OR CONTRIBUTORS BE LIABLE FOR ANY DIRECT, INDIRECT, * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, * BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS * OF USE, DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED * AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT * LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN * ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE * POSSIBILITY OF SUCH DAMAGE. * ****************************************************************************/ /**************************************************************************** * Included Files ****************************************************************************/ #include #include #include #include #include #include #include "sched/sched.h" #include "irq/irq.h" #if defined(CONFIG_SMP) || defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) /**************************************************************************** * Public Data ****************************************************************************/ #ifdef CONFIG_SMP /* This is the spinlock that enforces critical sections when interrupts are * disabled. */ volatile spinlock_t g_cpu_irqlock SP_SECTION = SP_UNLOCKED; /* Used to keep track of which CPU(s) hold the IRQ lock. */ volatile spinlock_t g_cpu_irqsetlock SP_SECTION; volatile cpu_set_t g_cpu_irqset SP_SECTION; #endif /**************************************************************************** * Private Data ****************************************************************************/ #ifdef CONFIG_SMP /* Handles nested calls to enter_critical section from interrupt handlers */ static uint8_t g_cpu_nestcount[CONFIG_SMP_NCPUS]; #endif /**************************************************************************** * Private Functions ****************************************************************************/ /**************************************************************************** * Name: irq_waitlock * * Description: * Spin to get g_irq_waitlock, 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-torun 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 inline bool irq_waitlock(int cpu) { #ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS FAR struct tcb_s *tcb = this_task(); /* 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(&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 are waiting for a spinlock */ sched_note_spinabort(tcb, &g_cpu_irqlock); #endif return false; } SP_DSB(); } /* We have g_cpu_irqlock! */ #ifdef CONFIG_SCHED_INSTRUMENTATION_SPINLOCKS /* Notify that we have the spinlock */ sched_note_spinlocked(tcb, &g_cpu_irqlock); #endif SP_DMB(); 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 increment 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_os_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_irqlock() 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). */ if (!irq_waitlock(cpu)) { /* We are in a deadlock condition due to a pending * pause request interrupt request. Break the * deadlock by handling the pause interrupt now. */ DEBUGVERIFY(up_cpu_paused(cpu)); } } /* In any event, the nesting count is now one */ g_cpu_nestcount[cpu] = 1; } } else { /* Normal tasking environment. */ /* Do we already have interrupts disabled? */ rtcb = this_task(); DEBUGASSERT(rtcb != NULL); 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. */ cpu = this_cpu(); 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. * * NOTE: This should never happen on architectures like * the Cortex-A; the inter-CPU interrupt (SGI) is not * maskable. */ up_irq_restore(ret); goto try_again; } /* The 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; #ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION /* Note that we have entered the critical section */ sched_note_csection(rtcb, true); #endif } } } /* Return interrupt status */ return ret; } #else /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) */ 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_os_initstate >= OSINIT_TASKLISTS) { FAR struct tcb_s *rtcb = this_task(); DEBUGASSERT(rtcb != NULL); /* Yes.. Note that we have entered the critical section */ sched_note_csection(rtcb, true); } /* 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_os_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. Release the spinlock. */ DEBUGASSERT(spin_islocked(&g_cpu_irqlock) && g_cpu_nestcount[cpu] == 1); spin_lock(&g_cpu_irqsetlock); /* Protects g_cpu_irqset */ if (g_cpu_irqset == 0) { spin_unlock(&g_cpu_irqlock); } spin_unlock(&g_cpu_irqsetlock); g_cpu_nestcount[cpu] = 0; } } else { FAR struct tcb_s *rtcb = this_task(); 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 { #ifdef CONFIG_SCHED_INSTRUMENTATION_CSECTION /* No.. Note that we have left the critical section */ sched_note_csection(rtcb, false); #endif /* Decrement our count on the lock. If all CPUs have * released, then unlock the spinlock. */ cpu = this_cpu(); DEBUGASSERT(spin_islocked(&g_cpu_irqlock) && (g_cpu_irqset & (1 << cpu)) != 0); rtcb->irqcount = 0; spin_clrbit(&g_cpu_irqset, cpu, &g_cpu_irqsetlock, &g_cpu_irqlock); /* Have all CPUs released the lock? */ if (!spin_islocked(&g_cpu_irqlock)) { /* Check if there are pending tasks and that pre-emption * is also enabled. * * REVISIT: Is there an issue here? up_release_pending() * must be called from within a critical section but here * we have just left the critical section. At least we * still have interrupts disabled on this CPU. */ if (g_pendingtasks.head != NULL && !spin_islocked(&g_cpu_schedlock)) { /* Release any ready-to-run tasks that have collected * in g_pendingtasks if the scheduler is not locked. * * NOTE: This operation has a very high likelihood of * causing this task to be switched out! * * REVISIT: Should this not be done while we are in the * critical section. */ up_release_pending(); } } } } } /* 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 /* defined(CONFIG_SCHED_INSTRUMENTATION_CSECTION) */ 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_os_initstate >= OSINIT_TASKLISTS) { FAR struct tcb_s *rtcb = this_task(); DEBUGASSERT(rtcb != NULL); /* Yes.. Note that we have left the critical section */ sched_note_csection(rtcb, false); } /* Restore the previous interrupt state. */ up_irq_restore(flags); } #endif #endif /* CONFIG_SMP || CONFIG_SCHED_INSTRUMENTATION_CSECTION*/