| 1 | /*
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| 2 | * Copyright (c) 2005 Jakub Jermar
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| 3 | * All rights reserved.
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| 4 | *
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| 5 | * Redistribution and use in source and binary forms, with or without
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| 6 | * modification, are permitted provided that the following conditions
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| 7 | * are met:
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| 8 | *
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| 9 | * - Redistributions of source code must retain the above copyright
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| 10 | * notice, this list of conditions and the following disclaimer.
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| 11 | * - Redistributions in binary form must reproduce the above copyright
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| 12 | * notice, this list of conditions and the following disclaimer in the
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| 13 | * documentation and/or other materials provided with the distribution.
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| 14 | * - The name of the author may not be used to endorse or promote products
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| 15 | * derived from this software without specific prior written permission.
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| 16 | *
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| 17 | * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR
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| 18 | * IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES
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| 19 | * OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED.
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| 20 | * IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT,
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| 21 | * INCIDENTAL, SPECIAL, EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT
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| 22 | * NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,
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| 23 | * DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY
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| 24 | * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
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| 25 | * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE OF
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| 26 | * THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
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| 27 | */
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| 28 |
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| 29 | /** @addtogroup generic
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| 30 | * @{
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| 31 | */
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| 32 |
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| 33 | /**
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| 34 | * @file preemption.c
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| 35 | * @brief Preemption control.
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| 36 | */
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| 37 |
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| 38 | #include <preemption.h>
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| 39 | #include <proc/scheduler.h>
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| 40 |
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| 41 |
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| 42 | /** Determines if we are executing an exception/interrupt handler. */
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| 43 | static bool in_exc_handler(void)
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| 44 | {
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| 45 | /* Err on the safe side until all exception processing code is audited. */
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| 46 | return true;
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| 47 | }
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| 48 |
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| 49 | /** Preemption was enabled. Calls scheduler(). */
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| 50 | void preemption_enabled_scheduler(void)
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| 51 | {
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| 52 | ASSERT(PREEMPTION_ENABLED);
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| 53 | ASSERT(PREEMPTION_NEEDED);
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| 54 |
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| 55 | /*
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| 56 | * Avoid a race between a thread about to invoke the scheduler()
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| 57 | * after checking THREAD->need_resched and an interrupt that
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| 58 | * occurs right after the check.
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| 59 | *
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| 60 | * Also ensures that code that relies on disabled interrupts
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| 61 | * to suppress preemption continues to work.
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| 62 | */
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| 63 | if (!interrupts_disabled() && !in_exc_handler()) {
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| 64 | preemption_clear_needed();
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| 65 | /* We may be preempted here, so we'll scheduler() again. Too bad. */
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| 66 | scheduler();
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| 67 | }
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| 68 | }
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| 69 |
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| 70 | /** Sets a flag to reschedule the next time preemption is enabled. */
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| 71 | void preemption_set_needed(void)
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| 72 | {
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| 73 | /* No need to disable interrupts. */
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| 74 | THE->preemption |= PREEMPTION_NEEDED_FLAG;
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| 75 | }
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| 76 |
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| 77 | /** Instructs not to reschedule immediately when preemption is enabled. */
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| 78 | void preemption_clear_needed(void)
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| 79 | {
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| 80 | /* No need to disable interrupts. */
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| 81 | THE->preemption &= ~PREEMPTION_NEEDED_FLAG;
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| 82 | }
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| 83 |
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| 84 | /** @}
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| 85 | */
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