[kvm-unit-tests PATCH] riscv: sbi: Fix timer delay measurement race

[Qingwei Hu]

The timer test samples the counter before checking timer_works in the
wait loop. If the timer interrupt arrives between these operations, the
handler sets timer_works and the loop exits with a timestamp taken before
the interrupt. That timestamp can precede the deadline, causing a false
"timer delay honored" failure in both the normal and masked IRQ tests.

Record the counter at the start of timer_irq_handler() and use it to
calculate the elapsed time. Keep the loop timestamp for timeout detection.

Fixes: 14fa12b1351c ("riscv: sbi: Add test for timer extension")
Signed-off-by: Qingwei Hu <qingwei.hu at bytedance.com>
---
 riscv/sbi.c | 4 +++-
 1 file changed, 3 insertions(+), 1 deletion(-)

diff --git a/riscv/sbi.c b/riscv/sbi.c
index 3b8aadce..a298228b 100644
--- a/riscv/sbi.c
+++ b/riscv/sbi.c
@@ -245,6 +245,7 @@ struct timer_info {
 	bool timer_irq_set;
 	bool timer_irq_cleared;
 	unsigned long timer_irq_count;
+	unsigned long irq_cycles;
 };
 
 static struct timer_info timer_info;
@@ -256,6 +257,7 @@ static bool timer_irq_pending(void)
 
 static void timer_irq_handler(struct pt_regs *regs)
 {
+	timer_info.irq_cycles = timer_get_cycles();
 	timer_info.timer_works = true;
 
 	if (timer_info.timer_irq_count < ULONG_MAX)
@@ -304,7 +306,7 @@ static void timer_check_set_timer(bool mask_timer_irq)
 	}
 
 	if (timer_info.timer_works) {
-		duration = end - begin;
+		duration = timer_info.irq_cycles - begin;
 		report(duration >= d && duration <= (d + margin), "timer delay honored%s", mask_test_str);
 	}
 
-- 
2.39.5