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SubjectRe: Is try_module_get buggy?
Date
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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