linux-kernel - Re: [Patch] restore the RCU callback to defer put_task

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Date:	Mon, 7 Aug 2006 20:05:24 -0700
From:	Bill Huey (hui) <billh@...ppy.monkey.org>
To:	Steven Rostedt <rostedt@...dmis.org>
Cc:	Robert Crocombe <rcrocomb@...il.com>, linux-kernel@...r.kernel.org,
	Ingo Molnar <mingo@...e.hu>,
	Thomas Gleixner <tglx@...utronix.de>,
	Darren Hart <dvhltc@...ibm.com>,
	"Bill Huey (hui)" <billh@...ppy.monkey.org>
Subject: Re: [Patch] restore the RCU callback to defer put_task_struct() Re: Problems with 2.6.17-rt8

On Mon, Aug 07, 2006 at 07:56:15PM -0700, Bill Huey wrote:
> On Thu, Aug 03, 2006 at 10:27:41AM -0400, Steven Rostedt wrote:
> 
> ...(output and commentary a log deleted)...
> 
> > This could also have a side effect that messes things up.
> > 
> > Unfortunately, right now I'm assigned to other tasks and I cant spend
> > much more time on this at the moment.  So hopefully, Ingo, Thomas or
> > Bill, or someone else can help you find the reason for this problem.
> 
> Steve and company,
> 
> Speaking of which, after talking to Steve about this and confirming this
> with a revert of changes. put_task_struct() can't deallocated memory from
> either the zone or SLAB cache without taking a sleeping lock. It can't
> be called directly from finish_task_switch to reap the thread because of
> that (violation in atomic).
> 
> It is for this reason the RCU call back to delay processing was put into
> place to reap threads and was, seemingly by accident, missing from
> patch-2.6.17-rt7 to -rt8. That is what broke it in the first place.
> 
> I tested it with a "make -j4" which triggers the warning and it they all
> go away now.
> 
> Reverse patch attached:

Resend with instrumentation code removed:

bill


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