From: Yang Jihong <yangjihong1@huawei.com>
To: Steven Rostedt <rostedt@goodmis.org>
Cc: <mingo@redhat.com>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] tracing: save cmdline only when task does not exist in savecmd for optimization
Date: Fri, 15 Oct 2021 09:27:35 +0800 [thread overview]
Message-ID: <3d07f3c9-3636-9563-fab5-603bfad4a3af@huawei.com> (raw)
In-Reply-To: <20211014103201.685d3647@gandalf.local.home>
Hi Steven,
On 2021/10/14 22:32, Steven Rostedt wrote:
> On Mon, 11 Oct 2021 19:50:18 +0800
> Yang Jihong <yangjihong1@huawei.com> wrote:
>
>> diff --git a/kernel/trace/trace.c b/kernel/trace/trace.c
>> index 7896d30d90f7..a795610a3b37 100644
>> --- a/kernel/trace/trace.c
>> +++ b/kernel/trace/trace.c
>> @@ -2427,8 +2427,11 @@ static int trace_save_cmdline(struct task_struct *tsk)
>> savedcmd->cmdline_idx = idx;
>> }
>>
>> - savedcmd->map_cmdline_to_pid[idx] = tsk->pid;
>> - set_cmdline(idx, tsk->comm);
>> + /* save cmdline only when task does not exist in savecmd */
>> + if (savedcmd->map_cmdline_to_pid[idx] != tsk->pid) {
>> + savedcmd->map_cmdline_to_pid[idx] = tsk->pid;
>> + set_cmdline(idx, tsk->comm);
>> + }
>>
>
> I now remember why I never did it this way. This breaks saving the command
> line when we do an exec.
>
> That is, just because mapped_pid == tsk->pid does not mean that the comm is
> the same.
>
If do an exec, the original process is replaced with a new binary.
Therefore, the command changes but the tsk->pid does not change.
Therefore, we need to savecmd here again?
Okay, I see. Thank you for the detailed explanation. :)
Thanks,
Jihong
> -- Steve
> .
>
prev parent reply other threads:[~2021-10-15 1:28 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-10-11 11:50 [PATCH] tracing: save cmdline only when task does not exist in savecmd for optimization Yang Jihong
2021-10-14 3:02 ` Steven Rostedt
2021-10-14 8:09 ` Yang Jihong
2021-10-14 14:32 ` Steven Rostedt
2021-10-15 1:27 ` Yang Jihong [this message]
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