sched/sem_waitirq: Fix semaphore wait interruption when MMU is in use #8918
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pussuw
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acassis
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Mar 28, 2023
This has been a long issue for me as it results in random crashes when asynchronous events occur when the idle process is active. The problem is that the kernel cannot access user memory, because the CPU status prevents it.
sem_t is user memory and the correct mappings are needed to perform the semaphore wait interruption. Otherwise either a page fault, or access to the WRONG address environment happens.
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jerpelea
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Mar 29, 2023
pkarashchenko
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Mar 29, 2023
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Summary
When MMU is in use, sem_waitirq fails because it tries to access sem_t (the waited object) which is user memory. This either results in page fault (crash) o access to the wrong address environment (crash later). This fixes the issue by:
Impact
Builds with MMU only (CONFIG_BUILD_KERNEL)
Testing
icicle:knsh
Linked with issue #8917
This is a way to fix the problem, but there might be an obvious alternative solution I could not think of