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new 3026e322d80 esp32s3_tickless: fix 32-bit overflow in
NSEC_2_CTICK/SEC_2_CTICK/USEC_2_CTICK
3026e322d80 is described below
commit 3026e322d80ea3c0ade464d22e3d5c7afcbe8f8c
Author: Felipe Moura <[email protected]>
AuthorDate: Mon Aug 31 12:01:03 2026 -0300
esp32s3_tickless: fix 32-bit overflow in
NSEC_2_CTICK/SEC_2_CTICK/USEC_2_CTICK
CONFIG_ESP32S3_TICKLESS hangs forever the first time a task calls a
sleep/timeout with a fractional-second component of roughly 134ms or
more (e.g. usleep(500000)) while another task is also pending a
timeout.
Root cause: NSEC_2_CTICK() computes ((nsec) * CTICK_PER_USEC) /
NSEC_PER_USEC. `nsec` (struct timespec's tv_nsec) is a 32-bit `long`,
and CTICK_PER_USEC is 16 (the S3's systimer runs at 16MHz), so the
multiplication overflows a 32-bit signed int for any tv_nsec at or
above INT32_MAX / 16 (~134,217,728 ns). The overflowed (negative)
result then gets added into up_timer_start()'s `uint64_t cpu_ticks`,
wrapping around to a value near UINT64_MAX. tickless_setcounter()
then programs the systimer alarm that many ticks in the future --
effectively never -- so nxsched_process_timer() is never called and
the waiting task sleeps forever.
Reproduced on real esp32s3-xiao hardware: apps/testing/ostest hung
indefinitely right after starting user_main(), whose first statement
is usleep(500000). Instrumented up_timer_start() to print its inputs
and observed exactly the described overflow (cpu_ticks close to
UINT64_MAX for tv_nsec=510000000). Confirmed root cause is the
concurrent-timeout case specifically: user_main's usleep() alone
works, and ostest_main's own usleep() alone works, but the two
together (matching ostest's actual task_create() + concurrent
usleep() pattern) reproduce the hang every time.
Fix: cast to uint64_t before multiplying in all three *_2_CTICK
macros, forcing 64-bit arithmetic throughout, matching how the
CTICK_2_* (division) macros are already overflow-safe.
Validated on esp32s3-xiao: with the fix, the full ostest suite (built
with CONFIG_ESP32S3_TICKLESS=y) runs past the point it used to hang
and completes end to end.
Note: while testing, ostest's own round-robin test (rr_test) failed
near the end of the run -- the two same-priority SCHED_RR threads did
not appear to interleave under tickless. That looks like a separate,
likely more architectural issue (time-slice preemption needs its own
periodic re-arm, independent of one-shot sleep timeouts) and is not
addressed by this fix; filing separately.
Signed-off-by: Felipe Moura <[email protected]>
---
arch/xtensa/src/esp32s3/esp32s3_tickless.c | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/arch/xtensa/src/esp32s3/esp32s3_tickless.c
b/arch/xtensa/src/esp32s3/esp32s3_tickless.c
index 3a3a1d7f5e7..d830ce4017f 100644
--- a/arch/xtensa/src/esp32s3/esp32s3_tickless.c
+++ b/arch/xtensa/src/esp32s3/esp32s3_tickless.c
@@ -76,9 +76,9 @@
#define CTICK_PER_SEC (ESP32S3_SYSTIMER_TICKS_PER_SEC)
#define CTICK_PER_USEC (CTICK_PER_SEC / USEC_PER_SEC)
-#define SEC_2_CTICK(s) ((s) * CTICK_PER_SEC)
-#define USEC_2_CTICK(us) ((us) * CTICK_PER_USEC)
-#define NSEC_2_CTICK(nsec) (((nsec) * CTICK_PER_USEC) / NSEC_PER_USEC)
+#define SEC_2_CTICK(s) ((uint64_t)(s) * CTICK_PER_SEC)
+#define USEC_2_CTICK(us) ((uint64_t)(us) * CTICK_PER_USEC)
+#define NSEC_2_CTICK(nsec) (((uint64_t)(nsec) * CTICK_PER_USEC) /
NSEC_PER_USEC)
#define CTICK_2_SEC(tick) ((tick) / CTICK_PER_SEC)
#define CTICK_2_USEC(tick) ((tick) / CTICK_PER_USEC)
@@ -246,6 +246,7 @@ static int IRAM_ATTR tickless_isr(int irq, void *context,
void *arg)
uint64_t unit_ticks = tickless_getcounter();
uint64_t alarm_ticks = tickless_getalarmvalue();
+
if (unit_ticks < alarm_ticks)
{
modifyreg32(SYSTIMER_CONF_REG, 0, SYSTIMER_TARGET0_WORK_EN);
