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Revert "Fix race condition when tracing is enabled (#95)" (#149)

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This reverts commit 61635d5b8b7ae1e783026f37eb66757509010130.
This commit is contained in:
Ming Yue 2020-08-28 14:17:29 -07:00 committed by GitHub
parent ce39ebe45b
commit 58ffcb1a6d
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1 changed files with 1 additions and 34 deletions
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35
portable/GCC/ARM_CR5/port.c
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@ -146,20 +146,6 @@
#define portTASK_RETURN_ADDRESS prvTaskExitError
#endif
/* Adding the necessary stuff in order to be able to determine from C code wheter or not the IRQs are enabled at the processor level (not interrupt controller level) */
#define GET_CPSR() \
( { u32 rval = 0U; \
__asm__ __volatile__ ( \
"mrs %0, cpsr\n"\
: "=r" ( rval ) \
); \
rval; \
} )
#define CPSR_IRQ_ENABLE_MASK 0x80U
#define IS_IRQ_DISABLED() ( { unsigned int val = 0; val = ( GET_CPSR() & CPSR_IRQ_ENABLE_MASK ) ? 1 : 0; val; } )
/*-----------------------------------------------------------*/
/*
@ -481,12 +467,6 @@ void vPortClearInterruptMask( uint32_t ulNewMaskValue )
uint32_t ulPortSetInterruptMask( void )
{
uint32_t ulReturn;
uint32_t wasIRQDisabled;
/* We keep track of if the IRQ are enabled in the CPU (as opposed to interrupts masked in the interrupt controller, like the intend of this function).
* This is very important because when the CPU is interrupted, among other things, the hardware clears the IRQ Enable bit in the CPSR of the IRQ CPU Mode in which
* we enter. */
wasIRQDisabled = IS_IRQ_DISABLED();
/* Interrupt in the CPU must be turned off while the ICCPMR is being
* updated. */
@ -505,20 +485,7 @@ uint32_t ulPortSetInterruptMask( void )
"isb \n"::: "memory" );
}
/* Just like this function returns a value of wether or not the interrupts where masked in the interrupt controller in order to avoid race condition when
* calling its matching vPortClearInterruptMask function, we needed a 'wasIRQDisabled' variable holding the state of the IRQ Enable bit in the CPSR in order
* to leave that bit in it's original state. Like mentioned above, hardware automatically clear the IRQEnable bit upon trapping into IRQ Mode, so the programmer
* cannot make assumption about it's state. Very rare, but very important race condition is avoided with this when this function is called in an ISR. The race
* condition in question was discovered when integrating tracealyzer code. Inside the function 'void vTaskSwitchContext( void )' in tasks.c, there is a macro 'traceTASK_SWITCHED_IN();'
* which gets replaced by something when using the tracing capabilities. That macro protects some critical section with matching calls to 'ulPortSetInterruptMask'
* and 'vPortClearInterruptMask'. At the time of calling those functions, the interrupt mask is not set in the interrupt controller, thus the only protecting barrier
* against the CPU traping into recursive interrupt was the IRQ Enable bit in the CPSR. By not taking it into acount, the very code that protects the CPU against
* critical section violation just enabled it to happen : A SysTick was waiting to happen, and calling 'portCPU_IRQ_ENABLE' would enable it to occur... Thus triggering a
* switch of context while already performing a switch context. */
if( !wasIRQDisabled )
{
portCPU_IRQ_ENABLE();
}
portCPU_IRQ_ENABLE();
return ulReturn;
}