Re: [PATCH] tracing: Add new_exec tracepoint

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Mon,  8 Apr 2024 11:01:54 +0200
Marco Elver <elver@google.com> wrote:

> Add "new_exec" tracepoint, which is run right after the point of no
> return but before the current task assumes its new exec identity.
> 
> Unlike the tracepoint "sched_process_exec", the "new_exec" tracepoint
> runs before flushing the old exec, i.e. while the task still has the
> original state (such as original MM), but when the new exec either
> succeeds or crashes (but never returns to the original exec).
> 
> Being able to trace this event can be helpful in a number of use cases:
> 
>   * allowing tracing eBPF programs access to the original MM on exec,
>     before current->mm is replaced;
>   * counting exec in the original task (via perf event);
>   * profiling flush time ("new_exec" to "sched_process_exec").
> 
> Example of tracing output ("new_exec" and "sched_process_exec"):

nit: "new_exec" name a bit stands out compared to other events, and hard to
expect it comes before or after "sched_process_exec". Since "begin_new_exec"
is internal implementation name, IMHO, it should not exposed to user.
What do you think about calling this "sched_prepare_exec" ?

Thank you,

> 
>   $ cat /sys/kernel/debug/tracing/trace_pipe
>       <...>-379     [003] .....   179.626921: new_exec: filename=/usr/bin/sshd pid=379 comm=sshd
>       <...>-379     [003] .....   179.629131: sched_process_exec: filename=/usr/bin/sshd pid=379 old_pid=379
>       <...>-381     [002] .....   180.048580: new_exec: filename=/bin/bash pid=381 comm=sshd
>       <...>-381     [002] .....   180.053122: sched_process_exec: filename=/bin/bash pid=381 old_pid=381
>       <...>-385     [001] .....   180.068277: new_exec: filename=/usr/bin/tty pid=385 comm=bash
>       <...>-385     [001] .....   180.069485: sched_process_exec: filename=/usr/bin/tty pid=385 old_pid=385
>       <...>-389     [006] .....   192.020147: new_exec: filename=/usr/bin/dmesg pid=389 comm=bash
>        bash-389     [006] .....   192.021377: sched_process_exec: filename=/usr/bin/dmesg pid=389 old_pid=389
> 
> Signed-off-by: Marco Elver <elver@google.com>
> ---
>  fs/exec.c                   |  2 ++
>  include/trace/events/task.h | 30 ++++++++++++++++++++++++++++++
>  2 files changed, 32 insertions(+)
> 
> diff --git a/fs/exec.c b/fs/exec.c
> index 38bf71cbdf5e..ab778ae1fc06 100644
> --- a/fs/exec.c
> +++ b/fs/exec.c
> @@ -1268,6 +1268,8 @@ int begin_new_exec(struct linux_binprm * bprm)
>  	if (retval)
>  		return retval;
>  
> +	trace_new_exec(current, bprm);
> +
>  	/*
>  	 * Ensure all future errors are fatal.
>  	 */
> diff --git a/include/trace/events/task.h b/include/trace/events/task.h
> index 47b527464d1a..8853dc44783d 100644
> --- a/include/trace/events/task.h
> +++ b/include/trace/events/task.h
> @@ -56,6 +56,36 @@ TRACE_EVENT(task_rename,
>  		__entry->newcomm, __entry->oom_score_adj)
>  );
>  
> +/**
> + * new_exec - called before setting up new exec
> + * @task:	pointer to the current task
> + * @bprm:	pointer to linux_binprm used for new exec
> + *
> + * Called before flushing the old exec, but at the point of no return during
> + * switching to the new exec.
> + */
> +TRACE_EVENT(new_exec,
> +
> +	TP_PROTO(struct task_struct *task, struct linux_binprm *bprm),
> +
> +	TP_ARGS(task, bprm),
> +
> +	TP_STRUCT__entry(
> +		__string(	filename,	bprm->filename	)
> +		__field(	pid_t,		pid		)
> +		__string(	comm,		task->comm	)
> +	),
> +
> +	TP_fast_assign(
> +		__assign_str(filename, bprm->filename);
> +		__entry->pid = task->pid;
> +		__assign_str(comm, task->comm);
> +	),
> +
> +	TP_printk("filename=%s pid=%d comm=%s",
> +		  __get_str(filename), __entry->pid, __get_str(comm))
> +);
> +
>  #endif
>  
>  /* This part must be outside protection */
> -- 
> 2.44.0.478.gd926399ef9-goog
> 


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>