Re: [kvm-unit-tests PATCH] arm: timer: Fix potential deadlock when waiting for interrupt

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On 29/07/19 11:28, Alexandru Elisei wrote:
> Commit 204e85aa9352 ("arm64: timer: a few test improvements") added a call
> to report_info after enabling the timer and before the wfi instruction. The
> uart that printf uses is emulated by userspace and is slow, which makes it
> more likely that the timer interrupt will fire before executing the wfi
> instruction, which leads to a deadlock.
> 
> An interrupt can wake up a CPU out of wfi, regardless of the
> PSTATE.{A, I, F} bits. Fix the deadlock by masking interrupts on the CPU
> before enabling the timer and unmasking them after the wfi returns so the
> CPU can execute the timer interrupt handler.
> 
> Suggested-by: Marc Zyngier <marc.zyngier@xxxxxxx>
> Signed-off-by: Alexandru Elisei <alexandru.elisei@xxxxxxx>
> ---
>  arm/timer.c | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/arm/timer.c b/arm/timer.c
> index 6f2ad1d76ab2..f2f60192ba62 100644
> --- a/arm/timer.c
> +++ b/arm/timer.c
> @@ -242,9 +242,11 @@ static void test_timer(struct timer_info *info)
>  	/* Test TVAL and IRQ trigger */
>  	info->irq_received = false;
>  	info->write_tval(read_sysreg(cntfrq_el0) / 100);	/* 10 ms */
> +	local_irq_disable();
>  	info->write_ctl(ARCH_TIMER_CTL_ENABLE);
>  	report_info("waiting for interrupt...");
>  	wfi();
> +	local_irq_enable();
>  	left = info->read_tval();
>  	report("interrupt received after TVAL/WFI", info->irq_received);
>  	report("timer has expired (%d)", left < 0, left);
> 

Queued, thanks.

Paolo



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