Inadequate locking in the esp_timer component allowed corruption
of the s_timers linked list:
1. timer_armed(timer) returns false
2. another task arms the timer and adds it to s_timers
3. the list is locked
4. the timer is inserted into s_timers again
The last step results in a loop in the s_timers list, which causes
an infinite loop when iterated. This change always locks the
list before checking if the timer is already armed avoiding
the data race.
Jens Gutermuth
Angus Gratton
Darian Leung
David Cermak
morris
Renz Bagaporo
Konstantin Kondrashov