95 lines
3.1 KiB
C
95 lines
3.1 KiB
C
/* malloc-lock.c. Lock malloc.
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*
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* Copyright (C) 2014, Authors
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*
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* Contributor Stefan Wallentowitz <stefan.wallentowitz@tum.de>
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*
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* The authors hereby grant permission to use, copy, modify, distribute,
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* and license this software and its documentation for any purpose, provided
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* that existing copyright notices are retained in all copies and that this
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* notice is included verbatim in any distributions. No written agreement,
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* license, or royalty fee is required for any of the authorized uses.
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* Modifications to this software may be copyrighted by their authors
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* and need not follow the licensing terms described here, provided that
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* the new terms are clearly indicated on the first page of each file where
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* they apply.
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*/
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#include <reent.h>
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#include <stdint.h>
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/* Lock calls from different cores, but allows recursive calls from the same
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* core. The lock is not only atomic to other cores calling malloc, but also
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* disables all external interrupts. This is necessary as it could otherwise
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* lead to a deadlock to interrupt while in malloc and then call it from an
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* exception. But as we want the exceptions to be flexible to use all library
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* calls and especially memory management this is necessary.
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*/
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// The lock. It is zero when unlocked and contains a unique value for each core.
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// This value is not the core id (to avoid id zero), but the pointer value of
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// the core specific struct _reent.
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volatile uint32_t _or1k_malloc_lock;
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// Count how often the current holder has entered the lock
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volatile uint32_t _or1k_malloc_lock_cnt;
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// The exception enable restore of the current mutex holder
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volatile uint32_t _or1k_malloc_lock_restore;
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extern uint32_t or1k_sync_cas(void *address, uint32_t compare, uint32_t swap);
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/**
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* Recursive lock of the malloc
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*/
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void __malloc_lock(struct _reent *ptr) {
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uint32_t restore;
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uint32_t id;
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// Each core is identified by its struct _reent pointer
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id = (uint32_t) ptr;
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// Disable timer and interrupt exception, save TEE and IEE flag
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// temporarily to restore them later on unlock
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restore = or1k_critical_begin();
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// We cannot be disturbed by an interrupt or timer exception from here
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// Check if we currently don't hold the lock
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if (_or1k_malloc_lock != id) {
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do {
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// Repeatedly check the lock until it is set to zero
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while (_or1k_malloc_lock != 0) {}
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// .. and then try to set it atomically. As this may
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// fail, we need to repeat this
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} while (or1k_sync_cas((void*) &_or1k_malloc_lock, 0, id) != 0);
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}
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// Store the TEE and IEE flags for later restore
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if (_or1k_malloc_lock_cnt == 0) {
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_or1k_malloc_lock_restore = restore;
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}
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// Increment counter. The lock may be accessed recursively
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_or1k_malloc_lock_cnt++;
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return;
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}
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void __malloc_unlock(struct _reent *ptr) {
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// Decrement counter. The lock may be unlocked recursively
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_or1k_malloc_lock_cnt--;
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// If this was the last recursive unlock call
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if(_or1k_malloc_lock_cnt == 0){
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// We need to temporarily store the value to avoid a race
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// condition between unlocking and reading restore
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uint32_t restore = _or1k_malloc_lock_restore;
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// unset lock
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_or1k_malloc_lock = 0;
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// Restore flags
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or1k_critical_end(restore);
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}
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return;
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}
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