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Running with CONFIG_DEBUG_SPINLOCK=y can trigger a BUG with the new IRQ stack code: BUG: spinlock lockup suspected on CPU#1 This is due to the IRQ_STACK_TO_TASK_STACK macro incorrectly retrieving the task stack pointer stashed at the top of the IRQ stack. Sayeth James: | Yup, this is what is happening. Its an off-by-one due to broken | thinking about how the stack works. My broken thinking was: | | > top ------------ | > | dummy_lr | <- irq_stack_ptr | > ------------ | > | x29 | | > ------------ | > | x19 | <- irq_stack_ptr - 0x10 | > ------------ | > | xzr | | > ------------ | | But the stack-pointer is decreased before use. So it actually looks | like this: | | > ------------ | > | | <- irq_stack_ptr | > top ------------ | > | dummy_lr | | > ------------ | > | x29 | <- irq_stack_ptr - 0x10 | > ------------ | > | x19 | | > ------------ | > | xzr | <- irq_stack_ptr - 0x20 | > ------------ | | The value being used as the original stack is x29, which in all the | tests is sp but without the current frames data, hence there are no | missing frames in the output. | | Jungseok Lee picked it up with a 32bit user space because aarch32 | can't use x29, so it remains 0 forever. The fix he posted is correct. This patch fixes the macro and adds some of this wisdom to a comment, so that the layout of the IRQ stack is well understood. Cc: James Morse <james.morse@arm.com> Reported-by: Jungseok Lee <jungseoklee85@gmail.com> Signed-off-by: Will Deacon <will.deacon@arm.com> |
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