From 81fec4bf328291c4b1517daee2ee49ee1b1a0c87 Mon Sep 17 00:00:00 2001
From: Guillaume Souchere <guillaume.souchere@espressif.com>
Date: Tue, 7 Jul 2026 12:50:50 +0200
Subject: [PATCH] fix(esp_timer): process ISR-dispatch timers in alarm thread
 on Linux
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On real hardware, ESP_TIMER_ISR callbacks run in a hardware interrupt
that preempts any FreeRTOS task. On the Linux simulator, there are no
real ISRs — the alarm is detected by a native pthread but was only
forwarded to the FreeRTOS timer_task via xTaskNotifyGive(). This meant
ISR-dispatch callbacks could be starved by higher-priority FreeRTOS
tasks, breaking components like the task watchdog that rely on
ISR-dispatch timers to detect scheduling starvation.

Move ISR-dispatch timer processing into the alarm pthread itself,
mirroring the hardware ISR path. The FreeRTOS timer_task is only
notified when no ISR-dispatch timer consumed the alarm. This is safe
because the Linux FreeRTOS port already handles vPortEnterCritical()
calls from non-FreeRTOS threads (bumps nesting counter without
blocking on scheduled-task checks).
---
 components/esp_timer/src/esp_timer.c            | 14 +-------------
 components/esp_timer/src/esp_timer_impl_linux.c | 11 +++--------
 2 files changed, 4 insertions(+), 21 deletions(-)

diff --git a/components/esp_timer/src/esp_timer.c b/components/esp_timer/src/esp_timer.c
index 5be84f50aa2..8790f5b6315 100644
--- a/components/esp_timer/src/esp_timer.c
+++ b/components/esp_timer/src/esp_timer.c
@@ -551,12 +551,6 @@ static void timer_task(void* arg)
     while (true) {
         ulTaskNotifyTake(pdTRUE, portMAX_DELAY);
         // all deferred events are processed at a time
-#if CONFIG_ESP_TIMER_IMPL_LINUX && CONFIG_ESP_TIMER_SUPPORTS_ISR_DISPATCH_METHOD
-        esp_timer_impl_try_to_set_next_alarm();
-        if (timer_process_alarm(ESP_TIMER_ISR)) {
-            continue;
-        }
-#endif
         timer_process_alarm(ESP_TIMER_TASK);
     }
 }
@@ -571,7 +565,6 @@ ESP_TIMER_IRAM_ATTR void esp_timer_isr_dispatch_need_yield(void)
 }
 #endif
 
-#ifndef CONFIG_ESP_TIMER_IMPL_LINUX
 static void ESP_TIMER_IRAM_ATTR timer_alarm_handler(void* arg)
 {
     BaseType_t xHigherPriorityTaskWoken = pdFALSE;
@@ -589,10 +582,9 @@ static void ESP_TIMER_IRAM_ATTR timer_alarm_handler(void* arg)
         vTaskNotifyGiveFromISR(s_timer_task, &xHigherPriorityTaskWoken);
     }
     if (xHigherPriorityTaskWoken == pdTRUE) {
-        portYIELD_FROM_ISR();
+        portYIELD_FROM_ISR(xHigherPriorityTaskWoken);
     }
 }
-#endif // !CONFIG_ESP_TIMER_IMPL_LINUX
 
 static ESP_TIMER_IRAM_ATTR inline bool is_initialized(void)
 {
@@ -646,11 +638,7 @@ esp_err_t esp_timer_init(void)
     }
 #endif // CONFIG_ESP_TIMER_ISR_AFFINITY_NO_AFFINITY
     if (err == ESP_OK) {
-#ifndef CONFIG_ESP_TIMER_IMPL_LINUX
         err = esp_timer_impl_init(&timer_alarm_handler);
-#else
-        err = esp_timer_impl_init(NULL);
-#endif
         if (err != ESP_OK) {
             ESP_EARLY_LOGE(TAG, "ISR init failed");
             deinit_timer_task();
diff --git a/components/esp_timer/src/esp_timer_impl_linux.c b/components/esp_timer/src/esp_timer_impl_linux.c
index a4f63e53d1a..7840ac40c2f 100644
--- a/components/esp_timer/src/esp_timer_impl_linux.c
+++ b/components/esp_timer/src/esp_timer_impl_linux.c
@@ -163,7 +163,7 @@ static esp_err_t program_timerfd(uint64_t deadline_us)
 
 static void *alarm_thread_func(void *arg)
 {
-    (void)arg;
+    intr_handler_t alarm_handler = (intr_handler_t)arg;
 
 #ifdef PR_SET_TIMERSLACK
     // Set timer slack to 1 ns for this thread.
@@ -219,10 +219,7 @@ static void *alarm_thread_func(void *arg)
                 continue;
             }
 
-            TaskHandle_t timer_task = esp_timer_impl_get_timer_task_handle();
-            if (timer_task != NULL) {
-                xTaskNotifyGive(timer_task);
-            }
+            alarm_handler(NULL);
         }
     }
 
@@ -300,8 +297,6 @@ esp_err_t esp_timer_impl_early_init(void)
 
 esp_err_t esp_timer_impl_init(intr_handler_t alarm_handler)
 {
-    (void)alarm_handler;
-
     timestamp_id[0] = UINT64_MAX;
     timestamp_id[1] = UINT64_MAX;
 
@@ -321,7 +316,7 @@ esp_err_t esp_timer_impl_init(intr_handler_t alarm_handler)
         return ESP_FAIL;
     }
 
-    int err = pthread_create(&s_alarm_thread, NULL, alarm_thread_func, NULL);
+    int err = pthread_create(&s_alarm_thread, NULL, alarm_thread_func, alarm_handler);
     if (err != 0) {
         ESP_LOGE(TAG, "Failed to create alarm thread: %s", strerror(err));