>
> Where is the prevention of module unload whilst a sysctl from a module is being read/written ?
>
> sysctl syscall is protected by BKL, but I can't see similar code for the cat >/proc/sys/...
... and that protection is worth nothing, since we copy data to/from
userland. Forget about BKL - it doesn't prevent races.
There is a shitload of rmmod (and plain "we remove the object" - it doesn't
have to be a module) races in that area. Composite trees _suck_. sysctls,
devfs, ddfs - whatever. If tree is served by several drivers - it's broken.
In case of sysctls I have an old patch that could be turned into something
working, but that will take a lot of changes in code that exports sysctls,
so that may be very painful.
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