On 01/20/2015, 04:26 PM, Josh Poimboeuf wrote:
> Add support for patching a function multiple times. If multiple patches
> affect a function, the function in the most recently enabled patch
> "wins". This enables a cumulative patch upgrade path, where each patch
> is a superset of previous patches.
>
> This requires restructuring the data a little bit. With the current
> design, where each klp_func struct has its own ftrace_ops, we'd have to
> unregister the old ops and then register the new ops, because
> FTRACE_OPS_FL_IPMODIFY prevents us from having two ops registered for
> the same function at the same time. That would leave a regression
> window where the function isn't patched at all (not good for a patch
> upgrade path).
>
> This patch replaces the per-klp_func ftrace_ops with a global klp_ops
> list, with one ftrace_ops per original function. A single ftrace_ops is
> shared between all klp_funcs which have the same old_addr. This allows
> the switch between function versions to happen instantaneously by
> updating the klp_ops struct's func_stack list. The winner is the
> klp_func at the top of the func_stack (front of the list).
>
> Signed-off-by: Josh Poimboeuf <jpoimboe@xxxxxxxxxx>
Reviewed-by: Jiri Slaby <jslaby@xxxxxxx>
But...
> @@ -267,16 +303,28 @@ static int klp_write_object_relocations(struct module *pmod,
>
> static void notrace klp_ftrace_handler(unsigned long ip,
> unsigned long parent_ip,
> - struct ftrace_ops *ops,
> + struct ftrace_ops *fops,
> struct pt_regs *regs)
> {
> - struct klp_func *func = ops->private;
> + struct klp_ops *ops;
> + struct klp_func *func;
> +
> + ops = container_of(fops, struct klp_ops, fops);
> +
> + rcu_read_lock();
> + func = list_first_or_null_rcu(&ops->func_stack, struct klp_func,
> + stack_node);
> + rcu_read_unlock();
> +
> + if (WARN_ON(!func))
> + return;
If it ever happens, the warn will drown the machine in the output splash.
WARN_ON_RATELIMIT?
thanks,
--
js
suse labs
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