Date: Fri, 11 Dec 2015 09:22:55 -0500
From: Steven Rostedt <rostedt@goodmis.org>
To: Minfei Huang <mnfhuang@gmail.com>
Cc: mhuang@redhat.com, linux-kernel@vger.kernel.org
Subject: Re: Some confusion about the period of updating new function in
Message-ID: <20151211092255.3bc7daec@gandalf.local.home>
In-Reply-To: <20151211105242.GA2826@dhcp-129-201.nay.redhat.com>
References: <20151211105242.GA2826@dhcp-129-201.nay.redhat.com>
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On Fri, 11 Dec 2015 18:52:42 +0800
Minfei Huang <mnfhuang@gmail.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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