Messages in this thread | | | From | Rusty Russell <> | Subject | Re: Is try_module_get buggy? | Date | Thu, 17 Jan 2008 14:09:39 +1100 |
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On Saturday 12 January 2008 15:35:27 rmingming wrote: > Hi, > I have a problem about the try_module_get function, I don't know if > someone removed the module just AFTER line 372, then what happens? Because > in this situation, the variable module will be incorrect, and > module_is_live function will lead to unpredicatable behaviour. > > 368 static inline int try_module_get(struct module *module) > 369 { > 370 int ret = 1; > 371 > 372 if (module) { > 373 unsigned int cpu = get_cpu(); > 374 if (likely(module_is_live(module))) > 375 local_inc(&module->ref[cpu].count); > 376 else > 377 ret = 0; > 378 put_cpu(); > 379 } > 380 return ret; > 381 }
Hi rminming,
try_module_get is designed to ensure that you don't call a function inside a module without a reference. Like any reference function, it cannot handle the case where the argument is invalid (or invalidated partway through the call).
In this case, the module pointer is usually inside a registered structure. The pointer will be valid until the structure is unregistered, which the calling code presumably prevents while it's doing a lookup.
Hope that clarifies, Rusty.
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