Module Observations
From: Srivatsa Vaddagiri
Date: Fri Jan 02 2004 - 08:22:10 EST
Hi,
I was going thr' module code and made some observations:
1. sys_init_module drops the module_mutex semaphore
before calling mod->init() function and later
reacquires it. After reacquiring, it marks
the module state as MODULE_STATE_LIVE.
In the window when mod->init() function is running,
isn't it possible that sys_delete_module (running
on some other CPU and trying to remove the _same_ module)
acquires the module_mutex sem and marks the module
state as MODULE_STATE_GOING?
Shouldn't sys_init_module check for
that possibility when it reacquires the semaphore after
calling mod->init function?
--- module.c.org Fri Jan 2 18:37:54 2004
+++ module.c Fri Jan 2 18:38:57 2004
@@ -1750,7 +1750,8 @@
/* Now it's a first class citizen! */
down(&module_mutex);
- mod->state = MODULE_STATE_LIVE;
+ if (likely(mod->state != MODULE_STATE_GOING))
+ mod->state = MODULE_STATE_LIVE;
/* Drop initial reference. */
module_put(mod);
module_free(mod, mod->module_init);
This off-course means that you are trying to insmod and rmmod
the same module simultaneously from different CPUs and hence
may not be practical.
2. try_module_get() and module_put()
try_module_get increments the local cpu's ref count for the module
and module_put decrements it.
Is it required that the caller call both these functions from the same CPU?
Otherwise, the total refcount for the module will be non-zero!
--
Thanks and Regards,
Srivatsa Vaddagiri,
Linux Technology Center,
IBM Software Labs,
Bangalore, INDIA - 560017
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