On Tue, 14 Sep 2021 17:41:34 -0400 Steven Rostedt <rostedt@xxxxxxxxxxx> wrote: > A better solution, that prevents having to do this, is to first change > the function fentry's to call the ftrace list loop function, that calls > the ftrace_ops list, and will call the direct call via the ops in the > loop. Have the ops->func call the new direct function (all will be > immediately affected). Update the entries, and then switch from the > loop back to the direct caller. An easy way to force the loop function to be called instead of the direct trampoline, is to register a stub ftrace_ops to each of the functions that the direct function attaches to. You can even share the hash in doing so. Having the ftrace_ops attached in the same locations as the direct trampoline, will force the loop function to be called (to call the stub ftrace_ops as well as the direct trampoline ftrace_ops helper). Then change the direct trampoline address, which will have the ftrace_ops helper use that direct trampoline immediately*. Then when you remove the ftrace_ops stub, it will update all the call sites to call the new direct trampoline directly. (*) not quite immediately, as there's no read memory barrier with the direct helper, so it may still be calling the old trampoline. But this shouldn't be an issue. If it is, then you would need to include some memory barrier synchronization. I'm curious to what the use case is for the multi direct modify interface is? -- Steve
