Messages in this thread | | | From | Jiri Olsa <> | Date | Sun, 19 Mar 2023 19:54:56 +0100 | Subject | Re: [PATCH 5/7] ftrace: Store direct called addresses in their ops |
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On Sun, Mar 19, 2023 at 01:54:43PM -0400, Steven Rostedt wrote: > On Sun, 19 Mar 2023 16:29:22 +0100 > Jiri Olsa <olsajiri@gmail.com> wrote: > > > > +++ b/kernel/trace/ftrace.c > > > @@ -2582,9 +2582,8 @@ ftrace_add_rec_direct(unsigned long ip, unsigned long addr, > > > static void call_direct_funcs(unsigned long ip, unsigned long pip, > > > struct ftrace_ops *ops, struct ftrace_regs *fregs) > > > { > > > - unsigned long addr; > > > + unsigned long addr = ops->direct_call; > > > > nice, should it be read with READ_ONCE ? > > Is there a "read tearing" too?
don't know, saw the comment in __modify_ftrace_direct and got curious why it's not in here.. feel free to ignore, I'll look it up
jirka
> > -- Steve > > > > > jirka > > > > > > > > - addr = ftrace_find_rec_direct(ip); > > > if (!addr) > > > return; > > > > > > @@ -5380,6 +5379,7 @@ int register_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > > > ops->func = call_direct_funcs; > > > ops->flags = MULTI_FLAGS; > > > ops->trampoline = FTRACE_REGS_ADDR; > > > + ops->direct_call = addr; > > > > > > err = register_ftrace_function_nolock(ops); > > > > > > @@ -5454,6 +5454,7 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > > > /* Enable the tmp_ops to have the same functions as the direct ops */ > > > ftrace_ops_init(&tmp_ops); > > > tmp_ops.func_hash = ops->func_hash; > > > + tmp_ops.direct_call = addr; > > > > > > err = register_ftrace_function_nolock(&tmp_ops); > > > if (err) > > > @@ -5475,6 +5476,8 @@ __modify_ftrace_direct(struct ftrace_ops *ops, unsigned long addr) > > > entry->direct = addr; > > > } > > > } > > > + /* Prevent store tearing if a trampoline concurrently accesses the value */ > > > + WRITE_ONCE(ops->direct_call, addr); > > > > > > mutex_unlock(&ftrace_lock);
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