fix/esp32s3-tickless-timeout-overflow - #20024
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xiaoxiang781216 merged 1 commit intoSep 1, 2026
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…C_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 <moura.fmo@gmail.com>
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Summary
CONFIG_ESP32S3_TICKLESShangs forever the first time a task sleepswith a fractional-second timeout of ~134ms or more (e.g.
usleep(500000)) while another task also has a pending timeout —e.g.
apps/testing/ostesthangs immediately, since that's exactlywhat
user_main()'s first statement does.Root cause
nsecis a 32-bitlongandCTICK_PER_USECis 16 (16MHz systimer),so
nsec * 16overflows a 32-bit signed int fortv_nsec >= ~134ms.The overflowed (negative) result gets added into
up_timer_start()'suint64_t cpu_ticks, wrapping to a value nearUINT64_MAX. Thesystimer alarm then gets programmed that many ticks in the future —
effectively never — so the sleeping task never wakes up.
SEC_2_CTICK/USEC_2_CTICKhave the same class of bug at higherthresholds.
Fix
Cast to
uint64_tbefore multiplying in all three macros, forcing64-bit arithmetic (matching the already-safe
CTICK_2_*macros).Also fixed a pre-existing nxstyle nit (missing blank line) in
tickless_isr(), next to the changed code.Testing
Board: Seeed XIAO ESP32-S3, built on current
master.up_timer_start()and confirmed the exactoverflow (
cpu_ticks=18446744073709121682for a ~500-700ms sleep).ostest(CONFIG_ESP32S3_TICKLESS=y) hangs right afterStarted user_main, reproducible every time from a clean flash.ostestsuite runs past that point and completes.sleep 3from NSH) keep correct timingbefore and after (3.06s measured).