Messages in this thread | | | Date | Tue, 19 Jul 2022 14:32:10 -0400 | From | Steven Rostedt <> | Subject | Re: [PATCH v4 bpf-next 2/4] ftrace: allow IPMODIFY and DIRECT ops on the same function |
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On Mon, 18 Jul 2022 16:59:51 +0000 Song Liu <songliubraving@fb.com> wrote:
> >> vim +/direct_mutex_locked +8197 kernel/trace/ftrace.c > >> > >> 8182 > >> 8183 /** > >> 8184 * register_ftrace_function - register a function for profiling > >> 8185 * @ops: ops structure that holds the function for profiling. > >> 8186 * > >> 8187 * Register a function to be called by all functions in the > >> 8188 * kernel. > >> 8189 * > >> 8190 * Note: @ops->func and all the functions it calls must be labeled > >> 8191 * with "notrace", otherwise it will go into a > >> 8192 * recursive loop. > >> 8193 */ > >> 8194 int register_ftrace_function(struct ftrace_ops *ops) > >> 8195 __releases(&direct_mutex) > >> 8196 { > >>> 8197 bool direct_mutex_locked = false; > >> 8198 int ret; > >> 8199 > >> 8200 ftrace_ops_init(ops); > >> 8201 > >> 8202 ret = prepare_direct_functions_for_ipmodify(ops); > >> 8203 if (ret < 0) > >> 8204 return ret; > >> 8205 else if (ret == 1) > >> 8206 direct_mutex_locked = true; > > > > Honestly, this is another horrible trick. Would it be possible to > > call prepare_direct_functions_for_ipmodify() with direct_mutex > > already taken?
Agreed. I'm not sure why I didn't notice this in the other versions. Probably was looking too much at the other logic. :-/
> > > > I mean something like: > > > > mutex_lock(&direct_mutex); > > > > ret = prepare_direct_functions_for_ipmodify(ops); > > if (ret) > > goto out: > > > > mutex_lock(&ftrace_lock); > > ret = ftrace_startup(ops, 0); > > mutex_unlock(&ftrace_lock); > > > > out: > > mutex_unlock(&direct_mutex); > > return ret; > > Yeah, we can actually do something like this. We can also move the > ops->flags & FTRACE_OPS_FL_IPMODIFY check to > register_ftrace_function(), so we only lock direct_mutex when when > it is necessary.
No need. Just take the direct_mutex, and perhaps add a:
lockdep_assert_held(&direct_mutex);
in the prepare_direct_functions_for_ipmodify().
This is far from a fast path to do any tricks in trying to optimize it.
-- Steve
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