From 1ccfd0b3cd19c44f17d8b99ae2e96866ddccebbe Mon Sep 17 00:00:00 2001
From: "J. Nick Koston" <nick@home-assistant.io>
Date: Sat, 21 Mar 2026 16:48:50 -1000
Subject: [PATCH] [logger] Fix race condition in task log buffer initialization

Move TaskLogBuffer allocation from init_log_buffer() (called at
DIAGNOSTICS priority) into the Logger constructor (called at
EARLY_INIT priority). This ensures the buffer exists before
global_logger is set, eliminating a window where another FreeRTOS
task could dereference a null log_buffer_ pointer.

Fixes crash: Guru Meditation Error: Core 0 panic'ed (Load access fault)
in TaskLogBuffer::send_message_thread_safe when a task logs before
init_log_buffer() is called.
---
 esphome/components/logger/__init__.py | 39 ++++++++++++++++-----------
 esphome/components/logger/logger.cpp  |  9 ++++++-
 esphome/components/logger/logger.h    |  6 +++--
 3 files changed, 36 insertions(+), 18 deletions(-)

diff --git a/esphome/components/logger/__init__.py b/esphome/components/logger/__init__.py
index a5601e6a8f..3da81e12a0 100644
--- a/esphome/components/logger/__init__.py
+++ b/esphome/components/logger/__init__.py
@@ -331,11 +331,27 @@ async def to_code(config: ConfigType) -> None:
     CORE.data.setdefault(CONF_LOGGER, {})[CONF_LEVEL] = level
     tx_buffer_size = config[CONF_TX_BUFFER_SIZE]
     cg.add_define("ESPHOME_LOGGER_TX_BUFFER_SIZE", tx_buffer_size)
-    log = cg.new_Pvariable(
-        config[CONF_ID],
-        baud_rate,
-    )
-    if CORE.is_esp32:
+    # Determine task log buffer size and define USE_ESPHOME_TASK_LOG_BUFFER early
+    # so the constructor can allocate the buffer immediately, preventing a race
+    # where another task logs before the buffer is initialized.
+    task_log_buffer_size = 0
+    if CORE.is_esp32 or CORE.is_libretiny or CORE.is_nrf52:
+        task_log_buffer_size = config[CONF_TASK_LOG_BUFFER_SIZE]
+    elif CORE.is_host:
+        task_log_buffer_size = 64  # Fixed 64 slots for host
+    if task_log_buffer_size > 0:
+        cg.add_define("USE_ESPHOME_TASK_LOG_BUFFER")
+        log = cg.new_Pvariable(
+            config[CONF_ID],
+            baud_rate,
+            task_log_buffer_size,
+        )
+    else:
+        log = cg.new_Pvariable(
+            config[CONF_ID],
+            baud_rate,
+        )
+    if CORE.is_esp32 or CORE.is_host:
         cg.add(log.create_pthread_key())
     # set_uart_selection() must be called before pre_setup() because
     # pre_setup() switches on uart_ to decide which hardware to initialize
@@ -364,17 +380,10 @@ async def _late_logger_init(config: ConfigType) -> None:
     log = await cg.get_variable(config[CONF_ID])
     level = config[CONF_LEVEL]
     baud_rate: int = config[CONF_BAUD_RATE]
-    if CORE.is_esp32 or CORE.is_libretiny or CORE.is_nrf52:
-        task_log_buffer_size = config[CONF_TASK_LOG_BUFFER_SIZE]
+    if CORE.using_zephyr:
+        task_log_buffer_size = config.get(CONF_TASK_LOG_BUFFER_SIZE, 0)
         if task_log_buffer_size > 0:
-            cg.add_define("USE_ESPHOME_TASK_LOG_BUFFER")
-            cg.add(log.init_log_buffer(task_log_buffer_size))
-            if CORE.using_zephyr:
-                zephyr_add_prj_conf("MPSC_PBUF", True)
-    elif CORE.is_host:
-        cg.add(log.create_pthread_key())
-        cg.add_define("USE_ESPHOME_TASK_LOG_BUFFER")
-        cg.add(log.init_log_buffer(64))  # Fixed 64 slots for host
+            zephyr_add_prj_conf("MPSC_PBUF", True)
 
     # Enable runtime tag levels if logs are configured or explicitly enabled
     logs_config = config[CONF_LOGS]
diff --git a/esphome/components/logger/logger.cpp b/esphome/components/logger/logger.cpp
index 497809cd2e..598af8117a 100644
--- a/esphome/components/logger/logger.cpp
+++ b/esphome/components/logger/logger.cpp
@@ -152,13 +152,20 @@ inline uint8_t Logger::level_for(const char *tag) {
   return this->current_level_;
 }
 
+#ifdef USE_ESPHOME_TASK_LOG_BUFFER
+Logger::Logger(uint32_t baud_rate, size_t task_log_buffer_size) : baud_rate_(baud_rate) {
+#else
 Logger::Logger(uint32_t baud_rate) : baud_rate_(baud_rate) {
+#endif
 #if defined(USE_ESP32) || defined(USE_LIBRETINY)
   this->main_task_ = xTaskGetCurrentTaskHandle();
 #elif defined(USE_ZEPHYR)
   this->main_task_ = k_current_get();
 #elif defined(USE_HOST)
-  this->main_thread_ = pthread_self();
+this->main_thread_ = pthread_self();
+#endif
+#ifdef USE_ESPHOME_TASK_LOG_BUFFER
+  this->init_log_buffer(task_log_buffer_size);
 #endif
 }
 #ifdef USE_ESPHOME_TASK_LOG_BUFFER
diff --git a/esphome/components/logger/logger.h b/esphome/components/logger/logger.h
index 8c38cadcbc..05b4cc21a7 100644
--- a/esphome/components/logger/logger.h
+++ b/esphome/components/logger/logger.h
@@ -143,9 +143,10 @@ enum UARTSelection : uint8_t {
  */
 class Logger final : public Component {
  public:
-  explicit Logger(uint32_t baud_rate);
 #ifdef USE_ESPHOME_TASK_LOG_BUFFER
-  void init_log_buffer(size_t total_buffer_size);
+  explicit Logger(uint32_t baud_rate, size_t task_log_buffer_size);
+#else
+  explicit Logger(uint32_t baud_rate);
 #endif
 #if defined(USE_ESPHOME_TASK_LOG_BUFFER) || (defined(USE_ZEPHYR) && defined(USE_LOGGER_UART_SELECTION_USB_CDC))
   void loop() override;
@@ -353,6 +354,7 @@ class Logger final : public Component {
   std::vector<LoggerLevelListener *> level_listeners_;  // Log level change listeners
 #endif
 #ifdef USE_ESPHOME_TASK_LOG_BUFFER
+  void init_log_buffer(size_t total_buffer_size);
   logger::TaskLogBuffer *log_buffer_{nullptr};  // Allocated once, never freed
 #endif