Le 2012-06-26 08:40, Mathieu Desnoyers a écrit :
>> +/*
>> + * lttng_uevent_set_handler - set handler functions for uevent
>> + *
>> + * Access to handler code is protected with rwlock in order to
>> + * prevent the optional module to be removed while in use.
>> + */
>> +
>> +void lttng_uevent_set_handler(write_ops_t handler)
>> +{
>> + write_lock(&uevent_rwlock);
>
> write lock not necessary.
>
> if (!lttng_uevent_set_handler)
> release refcount in prior handler's module.
>
> then:
> take a refcount on the module that contains the handler address.
> (explicit)
The function now looks like this:
void lttng_uevent_set_handler(struct file_operations *fops)
{
if (lttng_uevent_handler) {
module_put(lttng_uevent_handler->owner);
}
if (fops && try_module_get(fops->owner)) {
lttng_uevent_handler = fops;
return;
}
lttng_uevent_handler = NULL;
return;
}
The problem with this approach is that lttng_uevent can't be unloaded
anymore:
rmmod lttng_uevent
ERROR: Module lttng_uevent is in use
The module lttng_uevent can't be unloaded without unloading the module
lttng_tracer. The function module_exit of lttng_uevent is never called,
such that there is a chicken-and-egg situation. This problem was solved
by using rwlock to access the handler pointer. In the rare event when
unload module would occur while a trace event is recorded, the write
lock was preventing to change the handler pointer while it's in use. But
maybe there is another way to do it?
Thanks!
Francis Giraldeau
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