Re: [PATCH V4 1/1] rcu: introduce kfree_rcu()

Arnd Bergmann
2011-03-15T10:16:11Z

On Tuesday 15 March 2011 10:46:20 Lai Jiangshan wrote:
> +static __always_inline bool __is_kfree_rcu_offset(unsigned long offset)
> +{
> + return offset < 4096;
> +}

So this relies on the assumptions that

a) the rcu_head is within the first 4 KB of the data structure to be freed
b) no callback ever gets called in the first 4 KB of virtual address space

It's probably a reasonable assumption, but I think it should be documented
more explicitly, especially the first one. It's entirely possible that
an RCU managed data structure is larger than 4 KB.
Another alternative might be to encode the difference between a
function pointer and an offset in one of the lower bits of the address.

Arnd