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

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Message-ID: <20151211144635.GA4618@huangminfeis-MacBook-Pro.local>
Date:	Fri, 11 Dec 2015 22:46:35 +0800
From:	Minfei Huang <mnfhuang@...il.com>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	mhuang@...hat.com, linux-kernel@...r.kernel.org
Subject: Re: Some confusion about the period of updating new function in
 ftrace

On 12/11/15 at 09:22P, Steven Rostedt wrote:
> On Fri, 11 Dec 2015 18:52:42 +0800
> Minfei Huang <mnfhuang@...il.com> wrote:
> 
> > 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.
> 

Got it.

> > 
> > 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.

Thanks for your explanation.

Thanks
Minfei
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