xtimer/xtimer.c: xtimer_mutex_lock_timeout fix with short timeout

[JulianHolzwarth]

Tracking: pr #11660

Contribution description

Fixes BUG

This PR implements a new function to test xtimer_mutex_lock_timeout with a short timeout (spinning) and fixes the function xtimer_mutex_lock_timeout because without the fix in this PR the test fails.

This PR also implements a new function _mutex_remove_thread_from_waiting_queue. This function is implemented to remove all code out of xtimer_mutex_lock_timeout and _mutex_timeout that edits the mutex struct. The function _mutex_remove_thread_from_waiting_queue should be moved to mutex.c in the future to removed all code out of xtimer that edits the mutex struct.

Testing procedure

To test the bug fix run the test. To see the bug revert to commit: "tests/xtimer_mutex_lock_timeout: minimal xtimer_mutex_lock_timeout test" and run the test. (the test will fail)

BOARD=native make -C tests/xtimer_mutex_lock_timeout/ flash test

output:

...
> mutex_timeout_long_unlocked
starting test: xtimer mutex lock timeout
OK

> mutex_timeout_long_locked
mutex_timeout_long_locked
starting test: xtimer mutex lock timeout
OK

> mutex_timeout_long_locked_low
mutex_timeout_long_locked_low
starting test: xtimer mutex lock timeout with thread
threads = 2
THREAD low prio: start
MAIN THREAD: calling xtimer_mutex_lock_timeout
OK
threads = 3
MAIN THREAD: waiting for created thread to end
THREAD low prio: exiting low
threads = 2

> mutex_timeout_short_locked
mutex_timeout_short_locked
starting test: xtimer mutex lock timeout with short timeout and locked mutex
OK

> mutex_timeout_short_unlocked
mutex_timeout_short_unlocked
starting test: xtimer mutex lock timeout with short timeout and unlocked mutex
OK

output without fix:

...
> mutex_timeout_long_unlocked
starting test: xtimer mutex lock timeout
OK

> mutex_timeout_long_locked
mutex_timeout_long_locked
starting test: xtimer mutex lock timeout
OK

> mutex_timeout_long_locked_low
mutex_timeout_long_locked_low
starting test: xtimer mutex lock timeout with thread
threads = 2
THREAD low prio: start
MAIN THREAD: calling xtimer_mutex_lock_timeout
OK
threads = 3
MAIN THREAD: waiting for created thread to end
THREAD low prio: exiting low
threads = 2

> mutex_timeout_short_locked
mutex_timeout_short_locked
starting test: xtimer mutex lock timeout with short timeout and locked mutex
Timeout in expect script at "child.expect("OK")" (tests/xtimer_mutex_lock_timeout/tests/01-run.py:43)

...RIOT/tests/xtimer_mutex_lock_timeout/../../Makefile.include:735: recipe for target 'test' failed
make: *** [test] Error 1

Issues/PRs references

Tracking PR #11660

[JulianHolzwarth]

@MichelRottleuthner

[MichelRottleuthner]

handing the value of the volatile variable blocking to _mutex_lock will not have the desired effect here. The timeout might deschedule you right before the irq_disable of _mutex_lock is called, leaving you with a blocking call where actually a non-blocking lock should happen. Is there any reason for not just simply doing a non-blocking lock before setting up the timeout timer? This way you would always try to lock the mutex and if the timeout then happens between setting up the timer and locking it, is actually desired behavior to not lock it, right?

[JulianHolzwarth]

the timeout could happen before the mutex_lock but after the first non blocking mutex lock. Meaning there would be the same problem.
The problem with the irq_disable (interupt in function _mutex_lock but before irq_disable) will be fixed in the next PR. Tracking PR #11660
This PR fixes the problems with smaller timeouts.

[MichelRottleuthner]

Code and commits look fine, re-tested -> ACK