On 7/29/19 12:23 PM, Andrew Jones wrote:
> On Mon, Jul 29, 2019 at 10:28:52AM +0100, 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 <[email protected]>
>> Signed-off-by: Alexandru Elisei <[email protected]>
>> ---
>> 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);
>> --
>> 2.7.4
>>
> Reviewed-by: Andrew Jones <[email protected]>
>
> Thanks Alexandru. It now makes more sense to me that wfi wakes up on
> an interrupt, even when interrupts are masked, as it's clearly to
> avoid these types of races. I see we have the same type of race in
> arm/gic.c. I'll try to get around to fixing that at some point, unless
> somebody beats me to it :)
Something like this? Tested with gicv3-ipi.
diff --git a/arm/gic.c b/arm/gic.c
index ed5642e74f70..f0bd5739842a 100644
--- a/arm/gic.c
+++ b/arm/gic.c
@@ -220,12 +220,12 @@ static void ipi_enable(void)
#else
install_irq_handler(EL1H_IRQ, ipi_handler);
#endif
- local_irq_enable();
}
static void ipi_send(void)
{
ipi_enable();
+ local_irq_enable();
wait_on_ready();
ipi_test_self();
ipi_test_smp();
@@ -236,9 +236,13 @@ static void ipi_send(void)
static void ipi_recv(void)
{
ipi_enable();
+ local_irq_disable();
cpumask_set_cpu(smp_processor_id(), &ready);
- while (1)
+ while (1) {
+ local_irq_disable();
wfi();
+ local_irq_enable();
+ }
}
static void ipi_test(void *data __unused)
>
> drew
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