[PATCH v3] eal: fail initialization if TSC frequency is zero

[Stephen Hemminger]

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.

Also, clarify that DPDK TSC is stable and the same for all lcore's.
The comment in rte_cycles.h implied that it could be different per lcore.

Fixes: 040cf8a41187 ("eal: deduplicate timer functions")

Signed-off-by: Stephen Hemminger <stephen at networkplumber.org>
Acked-by: Bruce Richardson <bruce.richardson at intel.com>
---
v3 - rename set_tsc_freq to init_tsc_freq

 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, 20 insertions(+), 12 deletions(-)

diff --git a/lib/eal/common/eal_common_timer.c b/lib/eal/common/eal_common_timer.c
index bbf8b8b11b..67ede70c62 100644
--- a/lib/eal/common/eal_common_timer.c
+++ b/lib/eal/common/eal_common_timer.c
@@ -52,8 +52,8 @@ estimate_tsc_freq(void)
 	return RTE_ALIGN_MUL_NEAR(rte_rdtsc() - start, CYC_PER_10MHZ);
 }
 
-void
-set_tsc_freq(void)
+int
+init_tsc_freq(void)
 {
 	struct rte_mem_config *mcfg = rte_eal_get_configuration()->mem_config;
 	uint64_t freq;
@@ -65,18 +65,29 @@ 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();
+		if (freq == 0) {
+			EAL_LOG(ERR, "TSC frequency is too slow");
+			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..7da3783c9e 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 init_tsc_freq(void);
 
 /**
  * Get precise TSC frequency from system
diff --git a/lib/eal/freebsd/eal_timer.c b/lib/eal/freebsd/eal_timer.c
index d21ffa2694..b966c30258 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 init_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..c425ea4ed8 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 init_tsc_freq();
 }
diff --git a/lib/eal/windows/eal_timer.c b/lib/eal/windows/eal_timer.c
index 33cbac6a03..1e381ad673 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 init_tsc_freq();
 }
-- 
2.53.0