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lwIP mbox synchronization issue #5380

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pillip8282 opened this issue Dec 22, 2021 · 0 comments
Open

lwIP mbox synchronization issue #5380

pillip8282 opened this issue Dec 22, 2021 · 0 comments

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@pillip8282
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lwIP mbox synchronization issue

Description

mbox uses wait_send and wait_fetch to check that there is task which waits an event. It doesn't occur often, but problems can arise in special scenario.

Procedure

  1. Task A tried to fetch an data from mbox with timeout
  2. If mbox is empty then Task A increase wait_fetch with mutex protection
  3. Task A releases mutex and sys_arch_sem_wait(mail, timeout) to get an event.
  4. Time expires and task A exit from sys_arch_sem_wait()
  5. Context switching occurs, Task B post event with sys_arch_mbox_post()
  6. After task B enque data to mbox, it'll check whether send an event or not
  7. Task B sends an event because mbox was empty(first_msg == 1) and wait_fetch is not 0.
  8. After context switching task A lock mutex and decrease wait_fetch and exit the function.
  9. No task receive the event task B sent, so unexpected behavior can be happened.
pillip8282 added a commit to pillip8282/TizenRT that referenced this issue Jan 4, 2022
@pillip8282
lwip: add mbox sync testcase
b0ce1cc 
The commit played the issue reported to
Samsung#5380. The patch should pass
the testcase in mbox_sync.c
an4967 pushed a commit that referenced this issue Jan 4, 2022
@pillip8282 @an4967
lwip: add mbox sync testcase
7c6fde1 
The commit played the issue reported to
#5380. The patch should pass
the testcase in mbox_sync.c
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