linux-kernel - Re: [PATCH] tracing: ignore FTRACE_FL_DISABLED while walking dyn

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Date:   Mon, 14 Nov 2016 14:24:28 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Alexei Starovoitov <ast@...com>
Cc:     Dave Jones <davej@...emonkey.org.uk>,
        Martin KaFai Lau <kafai@...com>,
        <linux-kernel@...r.kernel.org>, <kernel-team@...com>
Subject: Re: [PATCH] tracing: ignore FTRACE_FL_DISABLED while walking
 dyn_ftrace records

On Mon, 7 Nov 2016 15:14:20 -0800
Alexei Starovoitov <ast@...com> wrote:

> ftrace_shutdown() checks for sanity of ftrace records
> and if dyn_ftrace->flags is not zero, it will warn.
> It can happen that 'flags' are set to FTRACE_FL_DISABLED at this point,
> since some module was loaded, but before ftrace_module_enable()
> cleared the flags for this module.
> 
> In other words the module.c is doing:
> ftrace_module_init(mod); // calls ftrace_update_code() that sets flags=FTRACE_FL_DISABLED
> ... // here ftrace_shutdown() is called that warns, since
> err = prepare_coming_module(mod); // didn't have a chance to clear FTRACE_FL_DISABLED
> 
> Fix it by ignoring disabled records.
> It's similar to what __ftrace_hash_rec_update() is already doing.
> 

Alexei,

Do you have a clear reproducer of this bug?

-- Steve

> Signed-off-by: Alexei Starovoitov <ast@...nel.org>
> ---
>  kernel/trace/ftrace.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/kernel/trace/ftrace.c b/kernel/trace/ftrace.c
> index 2050a7652a86..326498baab83 100644
> --- a/kernel/trace/ftrace.c
> +++ b/kernel/trace/ftrace.c
> @@ -2763,7 +2763,7 @@ static int ftrace_shutdown(struct ftrace_ops *ops, int command)
>  		struct dyn_ftrace *rec;
>  
>  		do_for_each_ftrace_rec(pg, rec) {
> -			if (FTRACE_WARN_ON_ONCE(rec->flags))
> +			if (FTRACE_WARN_ON_ONCE(rec->flags & ~FTRACE_FL_DISABLED))
>  				pr_warn("  %pS flags:%lx\n",
>  					(void *)rec->ip, rec->flags);
>  		} while_for_each_ftrace_rec();