Re: [PATCH] ftrace: Avoid quadratic symbol lookups in ftrace_module_enable()

[Steven Rostedt <rostedt@goodmis.org>]

On Sat, 03 Oct 2026 11:27:10 -0500
Lawrence Lin via B4 Relay <devnull+deduce.gmail.com@kernel.org> wrote:

> From: Lawrence Lin <deduce@gmail.com>
> 
> Since commit b39181f7c690 ("ftrace: Add FTRACE_MCOUNT_MAX_OFFSET to avoid
> adding weak function"), ftrace_module_enable() calls test_for_valid_rec()
> for every ftrace record of a module being loaded. test_for_valid_rec()
> resolves the record address with kallsyms_lookup(), and for a module
> address find_kallsyms_symbol() scans the whole symbol table of the module.
> Loading a module therefore costs O(records * symbols), all of it under
> ftrace_lock.

Honestly, I think we can revert commit b39181f7c690.

Since commit ef378c3b823385 ("scripts/sorttable: Zero out weak
functions in mcount_loc table"), I believe that commit has become
obsolete. I just kept it because I didn't want to add regressions.

It would be interesting if it actually triggers (finds something). If
it doesn't, then I think we should just remove that code instead of
adding more complexity to it.

-- Steve