linux-kernel - Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer

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Date:	Sat, 10 Aug 2013 09:26:15 +0800
From:	"zhangwei(Jovi)" <jovi.zhangwei@...il.com>
To:	Oleg Nesterov <oleg@...hat.com>
Cc:	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Namhyung Kim <namhyung.kim@....com>,
	Hyeoncheol Lee <cheol.lee@....com>,
	LKML <linux-kernel@...r.kernel.org>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	"zhangwei(Jovi)" <jovi.zhangwei@...wei.com>,
	Arnaldo Carvalho de Melo <acme@...stprotocols.net>
Subject: Re: [PATCH 10/13] tracing/uprobes: Fetch args before reserving a ring buffer

On Sat, Aug 10, 2013 at 12:20 AM, Oleg Nesterov <oleg@...hat.com> wrote:
>
> Sorry, I didn't read this series yet. Not that I think this needs my
> help, but I'll try to do this a later...
>
> On 08/09, Masami Hiramatsu wrote:
> >
> > I just concern using kmalloc() in the event handler.
>
> GFP_KERNEL should be fine for uprobe handler.
>
> However, iirc this conflicts with the patches from Jovi,
> "Support ftrace_event_file base multibuffer" adds rcu_read_lock()
> around uprobe_trace_print().

(Sorry about html text rejected by kernel.org, send again with plain text.)

Then we might need to call kmalloc before rcu_read_lock, also call kfree
after rcu_read_unlock.

And it's not needed to call kmalloc for each instances in multi-buffer
case, just
kmalloc once is enough.

I also have same concern about use kmalloc in uprobe handler, use kmalloc
in uprobe handler seems have a little overhead, why not pre-allocate one page
static memory for temp buffer(perhaps trace_uprobe based)? one page size
would be enough for all uprobe args storage, then we don't need to call
kmalloc in that "fast path".

Thanks.
>
>
> Steven, Jovi, what should we do with that patch? It seems that it
> was forgotten.
>
> I can take these patches into my ubprobes branch and then ask Ingo
> to pull. But this will complicate the routing of the new changes
> like this.
>
> Oleg.
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