linux-kernel - Re: Some confusion about the period of updating new function in

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Message-ID: <20151211092255.3bc7daec@gandalf.local.home>
Date:	Fri, 11 Dec 2015 09:22:55 -0500
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Minfei Huang <mnfhuang@...il.com>
Cc:	mhuang@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: Some confusion about the period of updating new function in

On Fri, 11 Dec 2015 18:52:42 +0800
Minfei Huang <mnfhuang@...il.com> wrote:

> ftrace
> Reply-To: 
> 
> Hi, Steven.
> 
> There is a confusion which blocks my step to go further for ftrace.
> 
> Does ftrace guarantee that the replaced function is finished while
> ftrace is replacing the functions? In the other word, is there a
> possible that new function starts to run, while old function is also
> running (maybe this function is called before replacing the function).

No there is no such guarantee. That is up to the function callbacks to
handle themselves.

> 
> Function schedule_on_each_cpu maybe fails to excute, if there is no
> enough memory to be allocated? Then kernel may be unstable, if ftrace
> continues, without handling the error, does it?
> 
> Previously, I posted a patch to fix this issue, and you nacked it.
> 
> [PATCH] workqueue: Add the allocation flags to function
> schedule_on_each_cpu_gfp

Ah that patch. Actually __GFP_NOFAIL is pretty much deprecated. The
real solution is to manually do the schedule on each CPU.

I can whip up a patch for that.

-- Steve

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