The function is not relevant any longer, remove it. Also remove
save_addrenv_t, the parameter taken by up_addrenv_restore.
Implement addrenv_select() / addrenv_restore() to handle the temporary
instantiation of address environments, e.g. when a process is being
created.
There is currently a big problem in the address environment handling which
is that the address environment is released too soon when the process is
exiting. The current MMU mappings will always be the exiting process's, which means
the system needs them AT LEAST until the next context switch happens. If
the next thread is a kernel thread, the address environment is needed for
longer.
Kernel threads "lend" the address environment of the previous user process.
This is beneficial in two ways:
- The kernel processes do not need an allocated address environment
- When a context switch happens from user -> kernel or kernel -> kernel,
the TLB does not need to be flushed. This must be done only when
changing to a different user address environment.
Another issue is when a new process is created; the address environment
of the new process must be temporarily instantiated by up_addrenv_select().
However, the system scheduler does not know that the process has a different
address environment to its own and when / if a context restore happens, the
wrong MMU page directory is restored and the process will either crash or
do something horribly wrong.
The following changes are needed to fix the issues:
- Add mm_curr which is the current address environment of the process
- Add a reference counter to safeguard the address environment
- Whenever an address environment is mapped to MMU, its reference counter
is incremented
- Whenever and address environment is unmapped from MMU, its reference
counter is decremented, and tested. If no more references -> drop the
address environment and release the memory as well
- To limit the context switch delay, the address environment is freed in
a separate low priority clean-up thread (LPWORK)
- When a process temporarily instantiates another process's address
environment, the scheduler will now know of this and will restore the
correct mappings to MMU
Why is this not causing more noticeable issues ? The problem only happens
under the aforementioned special conditions, and if a context switch or
IRQ occurs during this time.
Detach the address environment handling from the group structure to the
tcb. This is preparation to fix rare cases where the system (MMU) is left
without a valid page directory, e.g. when a process exits.
sim/rpserver
NuttShell (NSH) NuttX-12.0.0
server> cu
_assert: Current Version: NuttX server 12.0.0 3ead669e7a-dirty Feb 2 2023 23:53:48 sim
_assert: Assertion failed : at file: libs/libc/misc/lib_mutex.c:303 task: cu 0x5662fff4
Signed-off-by: chao an <anchao@xiaomi.com>
Here is a case how to use arg:
If application need do the ADC conversion as the same frequency and phase
of PWM, he can pass a semaphore as arg and then PWM driver will post the
semaphore in he start point of every period.
Signed-off-by: zhangchengqi <zhangchengqi@xiaomi.com>
This is preparation for moving address environments out of the group
structure into the tcb.
Why move ? Because the group is destroyed very early in the exit phase,
but the MMU mappings are needed until the context switch to the next
process is complete. Otherwise the MMU will lose its mappings and the
system will crash.
continue the follow work:
commit 43e7b13697
Author: Xiang Xiao <xiaoxiang@xiaomi.com>
Date: Sun Jan 22 19:31:32 2023 +0800
assert: Log the assertion expression in case of fail
Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>
