On Mon, Nov 14, 2011 at 12:24 PM, Johannes Berg
<johannes@xxxxxxxxxxxxxxxx> wrote:
> Hi,
>
>> > #define kfree_rcu(data, rcuhead) do { \
>> > void __kfree_rcu_fn(struct rcu_head *rcu_head) \
>> > { \
>> > void *___ptr; \
>> > ___ptr = container_of(rcu_head, typeof(*(data)), rcuhead);\
>> > kfree(___ptr); \
>> > } \
>> > call_rcu(&(data)->rcuhead, __kfree_rcu_fn); \
>> > } while (0)
>> >
>> >
>> > This works, thanks to gcc supporting nested functions, but has one major
>> > issue: any module using call_rcu() must have an rcu_barrier() in its
>> > module_exit() because __kfree_rcu_fn() might be called after the module
>> > is unloaded. For kfree_rcu() this isn't needed since the function called
>> > lives in the base kernel.
>>
>> This looks nice to me.
>
> :-)
>
>> > I played around with injecting a call to rcu_barrier() into module exit
>> > by modifying module_exit() but I couldn't make the CPP do that. Anyone
>> > else have any ideas?
>>
>> I played around with module_exit and modified the define into the
>> following. Now rcu_barrier() gets called on every module_exit. As
>> modules are not unloaded so often it should not hurd that this is also
>> done when unloading a module not using kfree_rcu().
>
> Ok.
>
>> #undef module_exit
>> #define module_exit(exitfn) \
>> void __exit __exit_rcu_barrier(void) \
>> { \
>> exitfn(); \
>> rcu_barrier(); \
>> } \
>> static inline exitcall_t __exittest(void) \
>> { return exitfn; } \
>> void cleanup_module(void) __attribute__((alias("__exit_rcu_barrier")));
>
>> Johannes are you fine with this?
>
> Frankly, I don't think I really understand it, but if it works, why not?
> I guess I could stick a printk into that function there to verify it ;-)
Can't say I get this either, but if it work and if documented really
well I'd gladly suck it in.
Luis
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