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audiocore: Fix small race window in get_fifo_read_value_blocking

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In theory, the FIFO interrupt could occur after getting the
fifo_read_value and reenabling interrupts, but before __wfi is called,
causing a deadlock. Fix this by calling __wfi with interrupts still
disabled. It will return immediately if an interrupt is pending.

Add two __nop to ensure that the CPU has enough instructions between
enabling interrupts and disabling them again at the top of the loop.

Signed-off-by: Matthias Blankertz <matthias@blankertz.org>
This commit is contained in:
Matthias Blankertz
2025-08-20 19:48:39 +02:00
parent f1de8c6c75
commit 6f155ebb55
1 changed files with 6 additions and 2 deletions
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8
software/modules/audiocore/module.c
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@@ -50,10 +50,14 @@ static uint32_t get_fifo_read_value_blocking(struct audiocore_obj *obj)
const long flags = save_and_disable_interrupts();
const uint32_t value = obj->fifo_read_value;
obj->fifo_read_value = 0;
restore_interrupts(flags);
if (value & AUDIOCORE_FIFO_DATA_FLAG)
if (value & AUDIOCORE_FIFO_DATA_FLAG) {
restore_interrupts(flags);
return value & ~AUDIOCORE_FIFO_DATA_FLAG;
}
__wfi();
restore_interrupts(flags);
__nop(); // Ensure at least two instructions between enable interrupts and subsequent disable
__nop();
}
}