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From:   Jeff Xie <xiehuan09@gmail.com>
Date:   Sun, 30 Jan 2022 10:37:28 +0800
Message-ID: <CAEr6+EBywRqWL-LSoH6Fx6tbkG6zFRMAAavoNVL79zdJuz5EBw@mail.gmail.com>
Subject: Re: [PATCH v7 0/4] trace: Introduce objtrace trigger to trace the
 kernel object
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Steven Rostedt <rostedt@goodmis.org>, mingo@redhat.com,
        Tom Zanussi <zanussi@kernel.org>, linux-kernel@vger.kernel.org
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Hi Masami,

On Wed, Jan 26, 2022 at 11:54 PM Masami Hiramatsu <mhiramat@kernel.org> wrote:
>
> Hi Jeff,
>
> On Wed, 19 Jan 2022 10:32:49 +0800
> Jeff Xie <xiehuan09@gmail.com> wrote:
>
> > > > Note: when change to use the ftrace_test_recursion_trylock, all the functions
> > > > will call the copy_from_kernel_nofault, I don't know where this is the problem now,
> > > > maybe should fall back to the usage in v6.
> > > >
> > > > for example:
> > > >
> > > > cat-118     [000] ...1.     1.458998: __bio_add_page <-bio_add_page object:0xffff88811a12e9e8 value:0x0
> > > > cat-118     [000] ...2.     1.458998: copy_from_kernel_nofault <-trace_object_events_call object:0xffff88811a12e9e8 value:0x1000
> > > > cat-118     [000] ...2.     1.458998: copy_from_kernel_nofault_allowed <-copy_from_kernel_nofault object:0xffff88811a12e9e8 value:0x1000
> > > > cat-118     [000] ...1.     1.458998: __rcu_read_lock <-xa_load object:0xffff88811a12e9e8 value:0x1000
> > > > cat-118     [000] ...2.     1.458998: copy_from_kernel_nofault <-trace_object_events_call object:0xffff88811a12e9e8 value:0x1000
> > > > cat-118     [000] ...2.     1.458998: copy_from_kernel_nofault_allowed <-copy_from_kernel_nofault object:0xffff88811a12e9e8 value:0x1000
> > > > cat-118     [000] ...1.     1.458998: __rcu_read_unlock <-xa_load object:0xffff88811a12e9e8 value:0x1000
> > > > cat-118     [000] ...3.     1.458998: copy_from_kernel_nofault <-trace_object_events_call object:0xffff88811a12e9e8 value:0x1000
> > > > cat-118     [000] ...3.     1.458998: copy_from_kernel_nofault_allowed <-copy_from_kernel_nofault object:0xffff88811a12e9e8 value:0x1000
> > > > ....
> > >
> > > Hmm, this is strange, but I got it is the expected behavior, since the
> > > ftrace_test_recursion_trylock() accepts one stage recursion for the
> > > first event in the interrupt as transition event.
>
> I think you should revert that change and back to your own per-cpu recursion
> flag instead of using ftrace_test_recursion_trylock().

Thanks, I will revert it.

> Thank you,
>
> --
> Masami Hiramatsu <mhiramat@kernel.org>

---
JeffXie