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Date:   Wed, 27 Jan 2021 17:29:50 -0500
From:   Steven Rostedt <rostedt@goodmis.org>
To:     Masami Hiramatsu <mhiramat@kernel.org>
Cc:     Jianlin Lv <Jianlin.Lv@arm.com>, Oleg Nesterov <oleg@redhat.com>,
        Ingo Molnar <mingo@redhat.com>, linux-kernel@vger.kernel.org
Subject: Re: [PATCH] tracing/kprobe: Fix to support kretprobe events on
 unloaded modules
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On Thu, 28 Jan 2021 00:37:51 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:

> Fix kprobe_on_func_entry() returns error code instead of false so that
> register_kretprobe() can return an appropriate error code.
> 
> append_trace_kprobe() expects the kprobe registration returns -ENOENT
> when the target symbol is not found, and it checks whether the target
> module is unloaded or not. If the target module doesn't exist, it
> defers to probe the target symbol until the module is loaded.
> 
> However, since register_kretprobe() returns -EINVAL instead of -ENOENT
> in that case, it always fail on putting the kretprobe event on unloaded
> modules. e.g.
> 
> Kprobe event:
> /sys/kernel/debug/tracing # echo p xfs:xfs_end_io >> kprobe_events
> [   16.515574] trace_kprobe: This probe might be able to register after target module is loaded. Continue.
> 
> Kretprobe event: (p -> r)
> /sys/kernel/debug/tracing # echo r xfs:xfs_end_io >> kprobe_events
> sh: write error: Invalid argument
> /sys/kernel/debug/tracing # cat error_log
> [   41.122514] trace_kprobe: error: Failed to register probe event
>   Command: r xfs:xfs_end_io
>              ^
> 
> To fix this bug, change kprobe_on_func_entry() to detect symbol lookup
> failure and return -ENOENT in that case. Otherwise it returns -EINVAL
> or 0 (succeeded, given address is on the entry).
> 
> Reported-by: Jianlin Lv <Jianlin.Lv@arm.com>
> Signed-off-by: Masami Hiramatsu <mhiramat@kernel.org>

Is this something that should go to stable? And if so, can you supply a
Fixes tag?

Thanks Masami,

-- Steve