Top 7 FreeRTOS Bugs That Crash Devices After 2–3 Days of Runtime

FreeRTOS Bugs often cause devices to crash after days of uptime due to task, queue, interrupt, and memory issues. Learn real causes and proven fixes.

FreeRTOS systems often run perfectly for hours or even days before suddenly crashing, hanging, or resetting without warning. These failures are rarely caused by obvious bugs. Instead, they come from subtle FreeRTOS issues that only appear after long runtime, real workloads, and unpredictable timing between tasks, interrupts, and memory.

In this deep-dive article, a senior embedded systems engineer with over 10 years of real-world FreeRTOS debugging experience breaks down the top 7 FreeRTOS bugs that crash devices after 2–3 days of runtime. This is not a beginner tutorial or academic theory. Every bug discussed here is based on real production failures seen in automotive, industrial, and IoT devices.

You will learn why common FreeRTOS bugs stay hidden during testing, how scheduling and heap behavior change over time, and why interrupt timing and task interaction are the real culprits behind long-runtime crashes. The article explains stack overflows that do not crash immediately, queue misuse involving QueueHandle_t, busy wait loops that slowly starve the scheduler, incorrect interrupt priorities, memory corruption caused by missing memory barriers, event group misuse, and CAN bus deadlocks under load.

Each bug includes a real-world scenario, why it passes initial testing, the exact failure mechanism, how it leads to a hard fault, hang, or watchdog reset, and how both beginners and experienced developers accidentally introduce it. You will also learn practical detection techniques using FreeRTOS backtrace analysis, coredumps, GDB, Segger Embedded Studio, tracing tools, and debugger workflows that actually work in production environments.

This article is written for real developers who debug real systems. If you are dealing with unexplained FreeRTOS crashes, long-term stability issues, or devices that fail only after days of uptime, this guide will help you recognize the patterns, confirm the root cause, and fix the problem correctly without guesswork.

Introduction

If you have worked with FreeRTOS long enough, you have seen this pattern.

The device boots fine.
Runs all tests.
Survives stress testing.
Customer deploys it.
Two or three days later, it locks up, resets, or goes silent.

Logs show nothing useful.
Watchdog resets keep happening.
Reboot fixes it… temporarily.

These are not beginner mistakes like forgetting to start the scheduler. These are long-runtime FreeRTOS bugs, and they are brutal to debug.

Why?

Because:

• They depend on timing
• They depend on task interaction
• They depend on memory behavior over time
• They almost never show up in short tests

I have debugged these issues on industrial controllers, automotive gateways, medical devices, and IoT hardware. The same patterns keep repeating.

This article is for:

• Beginners who want to avoid future pain
• Intermediate devs stuck chasing random resets
• Experienced engineers who want a clean freertos bug list they can cross-check against their system

Everything here comes from real debugging sessions, real post-mortems, and real devices sitting on my desk at 3 AM.

Why Long-Runtime Bugs Are Different in FreeRTOS

Scheduling hides problems

FreeRTOS is extremely forgiving at first.

Tasks run.
Queues pass data.
Events fire.
Interrupts work.

But scheduling creates time-based behavior, not immediate behavior. A task might run fine for 10,000 iterations before it finally collides with another task at just the wrong moment.

Heap behavior changes over time

Even if you never call pvPortMalloc() after startup, fragmentation can still happen indirectly.

Message buffers.
Timers.
Deferred interrupts.
Drivers doing hidden allocations.

Heap corruption rarely crashes immediately. It poisons memory slowly until something important gets overwritten.

Interrupt timing is never stable

What worked at low traffic fails under real load.

CAN bursts.
Button spam.
GPIO storms.
DDS or sensor interrupts firing faster than expected.

That is why debugging FreeRTOS issues always requires thinking in timelines, not just code paths.

Top 7 FreeRTOS Bugs That Crash Devices After 2–3 Days

🐞 Bug #1: Stack Overflow That Does Not Crash Immediately

Real-world scenario

A task handles protocol parsing. It has a local buffer, some structs, maybe a JSON decode. Everything works.

After two days, device resets with a freertos hardfault.

Why it passes initial testing

• Stack usage is almost enough
• Typical test messages are smaller
• Worst-case path is rare

FreeRTOS does not magically know your worst execution path.

Failure mechanism

Stack grows slowly over time.
Eventually it overwrites:

• Task control block
• Queue structures
• Event group memory

Now the scheduler trips over corrupted data.

Result

• Random reset
• Silent hang
• Hard fault inside the kernel

When you finally capture it, the freertos backtrace looks meaningless.

Beginner mistake

Assuming default stack sizes are fine.

Experienced mistake

Adding “just a bit more stack” without measuring.

How to detect it

• Enable stack overflow checking
• Use uxTaskGetStackHighWaterMark
• Inspect task stacks in freertos gdb or freertos segger embedded studio

If you ever use freertos+trace, stack usage spikes become obvious.

How to fix it

• Measure worst-case stack usage
• Avoid large local arrays
• Move buffers to static memory

This alone eliminates a shocking number of freertos bugs.

🐞 Bug #2: Queue Misuse with QueueHandle_t

Real-world scenario

You use queues everywhere. Sensor task pushes data. Processing task pulls it. Clean design.

Two days later, tasks stop responding.

Why it passes initial testing

Queues hide errors extremely well.

Sending to a deleted queue.
Using a stale freertos queuehandle_t.
Sending from ISR without the ISR-safe API.

All of these may work… until timing shifts.

Failure mechanism

Queue internal structures get corrupted.
Eventually scheduler walks invalid memory.
Boom.

Result

• Deadlock
• Kernel assert
• Hard fault

Often shows up as corrupted lists during debugging FreeRTOS.

Beginner mistake

Not checking return values from xQueueSend.

Experienced mistake

Passing queue handles across modules with no ownership rules.

How to detect it

• Enable asserts
• Validate queue handles
• Capture freertos coredump and inspect queue internals

How to fix it

• One owner per queue
• Clear lifecycle rules
• Use ISR APIs correctly

Queues are powerful, but they are not magic.

🐞 Bug #3: Busy Wait Instead of Proper Blocking

Real-world scenario

A task waits for hardware.

So someone writes:

while(!flag) {}

Classic freertos busy wait.

Why it passes initial testing

CPU is fast.
Load is low.
It “works”.

Failure mechanism

Busy wait:

• Starves lower priority tasks
• Prevents idle task from running
• Blocks memory cleanup
• Delays timers

Over days, timing drift builds up.

Result

• Watchdog resets
• Tasks never unblock
• System slowly degrades

Beginner mistake

Not understanding freertos blocking APIs.

Experienced mistake

Using busy wait to “optimize latency”.

How to detect it

• CPU usage stuck near 100%
• Idle task not running
• Trace shows starvation

How to fix it

Use:

• vTaskDelay
• xQueueReceive
• freertos wait for event

FreeRTOS is event-driven. Fight that and it fights back.

🐞 Bug #4: Incorrect Interrupt Priorities

Real-world scenario

GPIO interrupt fires on button press. CAN interrupt fires on bus traffic. Everything works.

After heavy load, system crashes.

Why it passes initial testing

Interrupt timing is light.
No nesting issues.

Failure mechanism

Wrong priority interrupts calling FreeRTOS APIs.

This violates kernel rules and corrupts internal state.

Result

• Scheduler corruption
• Random asserts
• freertos hardfault

Often blamed on hardware.

Beginner mistake

Ignoring priority rules in interrupts FreeRTOS.

Experienced mistake

Porting code from another RTOS without rechecking priorities.

How to detect it

• Audit ISR priorities
• Check which ISRs call RTOS APIs
• Debug with freertos debugger

How to fix it

• Follow max syscall interrupt priority rules
• Separate pure hardware ISRs from RTOS-aware ISRs

This bug alone explains many “it crashes only under load” cases.

🐞 Bug #5: Missing Memory Barriers

Real-world scenario

Shared data between ISR and task. Flags look correct. Logic is sound.

Still fails.

Why it passes initial testing

Compiler optimizations are minimal.
Timing is lucky.

Failure mechanism

Without a freertos memory barrier, compiler or CPU reorders memory access.

Task sees stale data.
ISR thinks task handled it.

Result

• Missed events
• Deadlocks
• Random behavior

Very hard to reproduce.

Beginner mistake

Not understanding memory ordering.

Experienced mistake

Assuming volatile is enough.

How to detect it

• Review shared variables
• Look for lock-free code
• Inspect assembly in freertos gdb

How to fix it

• Use FreeRTOS synchronization primitives
• Insert memory barriers where required
• Avoid lock-free sharing unless necessary

This is one of the sneakiest freertos bugs.

🐞 Bug #6: Event Group Misuse

Real-world scenario

Multiple tasks wait on events. Button interrupt sets a flag. Processing task waits.

Using freertos events everywhere feels elegant.

Why it passes initial testing

Low contention.
Clear logic.

Failure mechanism

• Event bits cleared too early
• Tasks waiting incorrectly with freertos wait for event
• Missed signals

Eventually tasks block forever.

Result

• Silent hang
• System appears alive but does nothing

Beginner mistake

Using events like queues.

Experienced mistake

Over-clever event bit combinations.

How to detect it

• Log event transitions
• Use trace tools
• Inspect blocked task lists

How to fix it

• Use events only for signaling
• Use queues for data
• Keep event logic simple

🐞 Bug #7: CAN Bus Deadlocks

Real-world scenario

CAN RX interrupt pushes frames. Processing task sends responses.

Works fine until bus traffic spikes.

Why it passes initial testing

Test traffic is clean.
No overload.

Failure mechanism

• RX ISR blocks indirectly
• TX queue fills
• Tasks wait on each other

Classic freertos can bus deadlock.

Result

• Bus silence
• Tasks blocked forever
• Watchdog reset

Beginner mistake

Doing too much inside CAN ISR.

Experienced mistake

Ignoring backpressure handling.

How to detect it

• Monitor queue depth
• Log ISR execution time
• Inspect blocked tasks

How to fix it

• Minimal ISR work
• Dedicated CAN worker task
• Proper flow control

Final Thoughts

If you are chasing a crash that happens after days, it is not random.

It is almost always:

• Stack
• Queues
• Interrupts
• Blocking
• Memory ordering
• Events
• Bus contention

Every single item in this freertos bug list has caused real devices to fail in the field.

If you take one thing from this article, let it be this:

FreeRTOS does exactly what you tell it to do.
Even when that destroys your system slowly.

Debug patiently.
Trace behavior over time.
Trust evidence, not assumptions.

And next time someone suggests a freertos bug bounty, you will know exactly where to look first.

FAQ on FreeRTOS Bugs

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