Mark esp_schedule IRAM_ATTR to make it ISR safe - this complements the suspend CONT via esp_yield pattern in esp_delay for early returning from delay due to external events. In libraries/ESP8266WiFi/src/ESP8266WiFiGeneric.cpp this is done from CBs, that are called from tools/sdk/lwip/include/lwip/dns.h (esp8266#6809)

dok-net · devyte · commit 916eb89b0754 · 2019-11-20T00:50:40.000-03:00
diff --git a/cores/esp8266/core_esp8266_main.cpp b/cores/esp8266/core_esp8266_main.cpp
@@ -108,8 +108,7 @@ extern "C" void __esp_yield() {
 
 extern "C" void esp_yield() __attribute__ ((weak, alias("__esp_yield")));
 
-extern "C" void esp_schedule() {
-    // always on CONT stack here
+extern "C" IRAM_ATTR void esp_schedule() {
     ets_post(LOOP_TASK_PRIORITY, 0, 0);
 }
 

Original file line number	Diff line number	Diff line change
`@@ -108,8 +108,7 @@ extern "C" void __esp_yield() {`
`108`	`108`
`109`	`109`	`extern "C" void esp_yield() __attribute__ ((weak, alias("__esp_yield")));`
`110`	`110`
`111`		`-extern "C" void esp_schedule() {`
`112`		`- // always on CONT stack here`
	`111`	`+extern "C" IRAM_ATTR void esp_schedule() {`
`113`	`112`	`ets_post(LOOP_TASK_PRIORITY, 0, 0);`
`114`	`113`	`}`
`115`	`114`