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https://github.com/zephyrproject-rtos/zephyr
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762ff2f428
The call to _arch_switch is a giant screaming sign inviting optimizer bugs. The code that appears before is what happened long ago when we were switched out, but the version that EXECUTED just now is actually in a different thread. So the assignment to _current before the switch actually assigned OUR thread (the "new_thread" of the old context!) to _current. But obviously the optimizer looks at that code and assumes that the _current which got assigned to the thread we were switching to long ago is still correct, and used it when retrieving the swap return value. Obviously the real bug here is that the _arch_switch() in question lacked a memory clobber (and it's getting one). But we can remove two lines, remove code from inside the interrupt lock and make the implementation more robust by moving the read to after the irq_unlock() (which generally also has a memory clobber). Signed-off-by: Andy Ross <andrew.j.ross@intel.com>
107 lines
2.3 KiB
C
107 lines
2.3 KiB
C
/*
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* Copyright (c) 2018 Intel Corporation
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*
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* SPDX-License-Identifier: Apache-2.0
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*/
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#ifndef ZEPHYR_KERNEL_INCLUDE_KSWAP_H_
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#define ZEPHYR_KERNEL_INCLUDE_KSWAP_H_
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#include <ksched.h>
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#include <kernel_arch_func.h>
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#ifdef CONFIG_STACK_SENTINEL
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extern void _check_stack_sentinel(void);
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#else
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#define _check_stack_sentinel() /**/
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#endif
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/* In SMP, the irq_lock() is a spinlock which is implicitly released
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* and reacquired on context switch to preserve the existing
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* semantics. This means that whenever we are about to return to a
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* thread (via either _Swap() or interrupt/exception return!) we need
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* to restore the lock state to whatever the thread's counter
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* expects.
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*/
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void _smp_reacquire_global_lock(struct k_thread *thread);
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void _smp_release_global_lock(struct k_thread *thread);
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/* context switching and scheduling-related routines */
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#ifdef CONFIG_USE_SWITCH
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/* New style context switching. _arch_switch() is a lower level
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* primitive that doesn't know about the scheduler or return value.
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* Needed for SMP, where the scheduler requires spinlocking that we
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* don't want to have to do in per-architecture assembly.
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*/
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static inline int _Swap(unsigned int key)
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{
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struct k_thread *new_thread, *old_thread;
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#ifdef CONFIG_EXECUTION_BENCHMARKING
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extern void read_timer_start_of_swap(void);
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read_timer_start_of_swap();
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#endif
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old_thread = _current;
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_check_stack_sentinel();
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#ifdef CONFIG_TRACING
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sys_trace_thread_switched_out();
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#endif
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new_thread = _get_next_ready_thread();
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if (new_thread != old_thread) {
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old_thread->swap_retval = -EAGAIN;
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#ifdef CONFIG_SMP
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_current_cpu->swap_ok = 0;
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new_thread->base.cpu = _arch_curr_cpu()->id;
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_smp_release_global_lock(new_thread);
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#endif
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_current = new_thread;
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_arch_switch(new_thread->switch_handle,
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&old_thread->switch_handle);
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}
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#ifdef CONFIG_TRACING
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sys_trace_thread_switched_in();
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#endif
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irq_unlock(key);
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return _current->swap_retval;
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}
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#else /* !CONFIG_USE_SWITCH */
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extern int __swap(unsigned int key);
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static inline int _Swap(unsigned int key)
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{
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int ret;
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_check_stack_sentinel();
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#ifndef CONFIG_ARM
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#ifdef CONFIG_TRACING
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sys_trace_thread_switched_out();
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#endif
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#endif
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ret = __swap(key);
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#ifndef CONFIG_ARM
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#ifdef CONFIG_TRACING
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sys_trace_thread_switched_in();
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#endif
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#endif
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return ret;
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}
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#endif
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#endif /* ZEPHYR_KERNEL_INCLUDE_KSWAP_H_ */
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