What version of RTL?
3.0pre8/9 do handle modules usage counts correctly.
Michael.
Hans de Goede ([EMAIL PROTECTED]) wrote:
> Hi all,
>
> I'm busy designing an realtime linux app using rtlinux and I encountered
> the following problem causing an oops, or if a module is loaded at the
> address of a previously loaded one even worse things. I have managed to
> reproduce it using something as simple as frank-app.
>
> I'll first describe my thought pattern that let me to the problem, to
> show that there is a deeper problem which is the cause of this. Then
> I'll describe the real problem, followed by an (ugly?!) solution to fix
> both.
>
> Problem:
> rtf_destroy is usually used from cleanup_module, cleanup_module is void,
> yet rtf_destroy can fail (when userspace progs still have the fifo
> open).
>
> This is usually fixed by just destroying all fifo's you use before
> creating them in init_module. I didn't want todo this since in our
> application multiple persons can write rttasks and I want to have the
> protection of rtf_create failing if multiple tasks accidentily try to
> use the same fifo.
>
> The fix for this is ofcourse to have a well defined list of fifo's so
> that people won't try to use the same fifo.
>
> But I still thought that having todo rtf_destroy in init_module is not
> clean, and that there really should be a way to INC_MOD_USE_COUNT of
> your module/task when the user opens an rtfifo you've created, so that
> cleanup_module won't be called with the fifo is open by a userspace
> program.
>
> While searching for a workaround since I didn't want to change the
> rt_fifo.c code I encountered the following scenario:
>
> rt_task.c:
>
> init_module
> {
> rtf_create(1, whatever)
> rtf_create_handler(1, my_handler)
> }
>
>
> cleanup_module
> {
> rtf_destroy(1)
> }
>
> now do the following:
> -insmod rt_task.o -> fifo is created successfully
> -have a task open /dev/rtf1
> -rmmod rt_task.o -> fifo is not destroyed because it is open
> -have the task write to /dev/rtf1 -> my_handler (which is no longer) is
> called -> oops (or worse if a new / other module was loaded at that
> address
>
> IMHO the only correct fix is to INC_MOD_USE_COUNT of rt_task.o when
> /dev/rtf1 is opened, and DEC it again when it is closed. This would
> require a callback function argument to rtf_create, since you can only
> use INC_MOD_USE_COUNT from the actual module itself. This seems to be
> the correct thing todo always, and is a must have when using handlers
> since in essence the rt_fifo module has a reference to the rt_task
> module, and hence the rt_task module is in use.
>
> For the unbelievers this can easiliy be recreated with the frank
> example,
>
> insmod frank_module.o
> ./frank_app&
> rmmod frank_module
>
> Now just wait for all the selects in frank_app to time out (about 100
> seconds) then it will try to write to /dev/rtf3 which has a handler to
> stop the tasks -> oops.
>
> Regards,
>
> Hans
>
> p.s.
>
> I'm working on a fix and I'll mail it as a patch to the list when I'm
> ready.
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