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Previously, this was subject to races incrementing/decrementing the counter variable pendsv_lock. Technically, all that's needed here would be to make pendsv_lock an atomic counter. This implementation fulfils a stronger guarantee: it also provides mutual exclusion for the core which calls pendsv_suspend(). This is because the current use of pendsv_suspend/resume in MicroPython is to ensure exclusive access to softtimer data structures, and this does require mutual exclusion. The conceptually cleaner implementation would split the mutual exclusion part out into a softtimer-specific spinlock, but this increases the complexity and doesn't seem like it makes for a better implementation in the long run. This work was funded through GitHub Sponsors. Signed-off-by: Angus Gratton <angus@redyak.com.au>
103 lines
3.5 KiB
C
103 lines
3.5 KiB
C
/*
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* This file is part of the MicroPython project, http://micropython.org/
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*
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* The MIT License (MIT)
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*
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* Copyright (c) 2022 Damien P. George
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*
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* Permission is hereby granted, free of charge, to any person obtaining a copy
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* of this software and associated documentation files (the "Software"), to deal
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* in the Software without restriction, including without limitation the rights
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* to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
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* copies of the Software, and to permit persons to whom the Software is
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* furnished to do so, subject to the following conditions:
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*
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* The above copyright notice and this permission notice shall be included in
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* all copies or substantial portions of the Software.
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*
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* THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
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* IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
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* FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
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* AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
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* LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
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* OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
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* THE SOFTWARE.
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*/
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#include <assert.h>
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#include "pico/mutex.h"
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#include "py/mpconfig.h"
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#include "pendsv.h"
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#include "RP2040.h"
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#if MICROPY_PY_NETWORK_CYW43
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#include "lib/cyw43-driver/src/cyw43_stats.h"
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#endif
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static pendsv_dispatch_t pendsv_dispatch_table[PENDSV_DISPATCH_NUM_SLOTS];
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static recursive_mutex_t pendsv_mutex;
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void pendsv_init(void) {
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recursive_mutex_init(&pendsv_mutex);
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}
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void pendsv_suspend(void) {
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// Recursive Mutex here as either core may call pendsv_suspend() and expect
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// both mutual exclusion (other core can't enter pendsv_suspend() at the
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// same time), and that no PendSV handler will run.
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recursive_mutex_enter_blocking(&pendsv_mutex);
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}
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void pendsv_resume(void) {
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recursive_mutex_exit(&pendsv_mutex);
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// Run pendsv if needed. Find an entry with a dispatch and call pendsv dispatch
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// with it. If pendsv runs it will service all slots.
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int count = PENDSV_DISPATCH_NUM_SLOTS;
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while (count--) {
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if (pendsv_dispatch_table[count]) {
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pendsv_schedule_dispatch(count, pendsv_dispatch_table[count]);
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break;
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}
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}
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}
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void pendsv_schedule_dispatch(size_t slot, pendsv_dispatch_t f) {
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pendsv_dispatch_table[slot] = f;
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if (pendsv_mutex.enter_count == 0) {
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// There is a race here where other core calls pendsv_suspend() before
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// ISR can execute, but dispatch will happen later when other core
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// calls pendsv_resume().
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SCB->ICSR = SCB_ICSR_PENDSVSET_Msk;
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} else {
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#if MICROPY_PY_NETWORK_CYW43
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CYW43_STAT_INC(PENDSV_DISABLED_COUNT);
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#endif
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}
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}
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// PendSV interrupt handler to perform background processing.
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void PendSV_Handler(void) {
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if (!recursive_mutex_try_enter(&pendsv_mutex, NULL)) {
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// Failure here means core 1 holds pendsv_mutex. ISR will
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// run again after core 1 calls pendsv_resume().
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return;
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}
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// Core 0 should not already have locked pendsv_mutex
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assert(pensv_mutex.enter_count == 1);
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#if MICROPY_PY_NETWORK_CYW43
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CYW43_STAT_INC(PENDSV_RUN_COUNT);
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#endif
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for (size_t i = 0; i < PENDSV_DISPATCH_NUM_SLOTS; ++i) {
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if (pendsv_dispatch_table[i] != NULL) {
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pendsv_dispatch_t f = pendsv_dispatch_table[i];
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pendsv_dispatch_table[i] = NULL;
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f();
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}
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}
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recursive_mutex_exit(&pendsv_mutex);
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}
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