Re: [PATCH v2] eal: fail initialization if TSC frequency is zero

[Bruce Richardson <bruce.richardson@intel.com>]

On Mon, Sep 28, 2026 at 04:15:58PM -0700, Stephen Hemminger wrote:
> Many parts of DPDK will fail with divide by zero and
> other errors if the initialization logic ever TSC hz was ever
> determined to be zero. This might happen on a broken get_tsc_freq_arch()
> or bad emulation in QEMU.
> 
> If TSC hz is zero, log the error and propagate back to
> fail rte_eal_init().
> 
> This fix doesn't need to go to stable since it is a purely
> theoretical problem; we aren't getting divide by zero reports
> from users.
> 

How was this discovered? Is there a coverity issue id, or was it just AI
discovered?

> Fixes: 040cf8a41187 ("eal: deduplicate timer functions")
> 
> Signed-off-by: Stephen Hemminger <stephen@networkplumber.org>
> ---
> v2 - cleanups: mostly squash useless comments
> 

Code looks generally ok to me.

>  lib/eal/common/eal_common_timer.c    | 19 ++++++++++++++++---
>  lib/eal/common/eal_private.h         |  2 +-
>  lib/eal/freebsd/eal_timer.c          |  3 +--
>  lib/eal/include/generic/rte_cycles.h |  2 +-
>  lib/eal/linux/eal_timer.c            |  3 +--
>  lib/eal/windows/eal_timer.c          |  3 +--
>  6 files changed, 21 insertions(+), 11 deletions(-)
> 
> diff --git a/lib/eal/common/eal_common_timer.c b/lib/eal/common/eal_common_timer.c
> index bbf8b8b11b..e9f8b56b59 100644
> --- a/lib/eal/common/eal_common_timer.c
> +++ b/lib/eal/common/eal_common_timer.c
> @@ -52,7 +52,7 @@ estimate_tsc_freq(void)
>  	return RTE_ALIGN_MUL_NEAR(rte_rdtsc() - start, CYC_PER_10MHZ);
>  }
>  
> -void
> +int
>  set_tsc_freq(void)
>  {
>  	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
> @@ -65,18 +65,31 @@ set_tsc_freq(void)
>  		 * systems where arch-specific frequency detection is not
>  		 * available.
>  		 */
> +		if (mcfg->tsc_hz == 0) {
> +			EAL_LOG(ERR, "Primary process TSC frequency is zero");
> +			return -1;
> +		}
> +
>  		eal_tsc_resolution_hz = mcfg->tsc_hz;
> -		return;
> +		return 0;
>  	}
>  
>  	freq = get_tsc_freq_arch();
>  	freq = get_tsc_freq(freq);
> -	if (!freq)
> +	if (freq == 0) {
>  		freq = estimate_tsc_freq();
>  
> +		/* Check if TSC is not moving */
> +		if (freq == 0) {
> +			EAL_LOG(ERR, "TSC frequency is not changing");
> +			return -1;
> +		}
> +	}
> +
>  	EAL_LOG(DEBUG, "TSC frequency is ~%" PRIu64 " KHz", freq / 1000);
>  	eal_tsc_resolution_hz = freq;
>  	mcfg->tsc_hz = freq;
> +	return 0;
>  }
>  
>  RTE_EXPORT_SYMBOL(rte_delay_us_callback_register)
> diff --git a/lib/eal/common/eal_private.h b/lib/eal/common/eal_private.h
> index 6340bab8be..952cb5a03e 100644
> --- a/lib/eal/common/eal_private.h
> +++ b/lib/eal/common/eal_private.h
> @@ -409,7 +409,7 @@ int eal_cpu_detected(unsigned lcore_id);
>   *
>   * This function is private to the EAL.
>   */
> -void set_tsc_freq(void);
> +int set_tsc_freq(void);
>  

One minor suggestion: set_tsc_freq name implies that the user passes in a
value to be set. I wonder if "init_tsc_freq" might be a better name here,
since you are updating all calls anyway to handle an error return.

>  /**
>   * Get precise TSC frequency from system
> diff --git a/lib/eal/freebsd/eal_timer.c b/lib/eal/freebsd/eal_timer.c
> index d21ffa2694..84127d876b 100644
> --- a/lib/eal/freebsd/eal_timer.c
> +++ b/lib/eal/freebsd/eal_timer.c
> @@ -65,6 +65,5 @@ get_tsc_freq(uint64_t arch_hz)
>  int
>  rte_eal_timer_init(void)
>  {
> -	set_tsc_freq();
> -	return 0;
> +	return set_tsc_freq();
>  }
> diff --git a/lib/eal/include/generic/rte_cycles.h b/lib/eal/include/generic/rte_cycles.h
> index 7cfd51f0eb..f8e1cde332 100644
> --- a/lib/eal/include/generic/rte_cycles.h
> +++ b/lib/eal/include/generic/rte_cycles.h
> @@ -34,7 +34,7 @@ extern enum timer_source eal_timer_source;
>   * Get the measured frequency of the RDTSC counter
>   *
>   * @return
> - *   The TSC frequency for this lcore
> + *   The TSC frequency for all lcores, always non-zero
>   */
>  uint64_t
>  rte_get_tsc_hz(void);
> diff --git a/lib/eal/linux/eal_timer.c b/lib/eal/linux/eal_timer.c
> index 39f975b6b9..bccff60ff8 100644
> --- a/lib/eal/linux/eal_timer.c
> +++ b/lib/eal/linux/eal_timer.c
> @@ -99,6 +99,5 @@ rte_eal_timer_init(void)
>  
>  	eal_timer_source = EAL_TIMER_TSC;
>  
> -	set_tsc_freq();
> -	return 0;
> +	return set_tsc_freq();
>  }
> diff --git a/lib/eal/windows/eal_timer.c b/lib/eal/windows/eal_timer.c
> index 33cbac6a03..aec8ea854d 100644
> --- a/lib/eal/windows/eal_timer.c
> +++ b/lib/eal/windows/eal_timer.c
> @@ -94,6 +94,5 @@ get_tsc_freq(uint64_t arch_hz)
>  int
>  rte_eal_timer_init(void)
>  {
> -	set_tsc_freq();
> -	return 0;
> +	return set_tsc_freq();
>  }
> -- 
> 2.53.0
>