Date: Thu, 23 Oct 2014 15:37:59 -0400
From: Dave Jones <davej@redhat.com>
To: "Paul E. McKenney" <paulmck@linux.vnet.ibm.com>
Cc: Linux Kernel <linux-kernel@vger.kernel.org>, htejun@gmail.com,
        oleg@redhat.com
Subject: Re: rcu_preempt detected stalls.
Message-ID: <20141023193759.GA14188@redhat.com>
Mail-Followup-To: Dave Jones <davej@redhat.com>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Linux Kernel <linux-kernel@vger.kernel.org>, htejun@gmail.com,
	oleg@redhat.com
References: <20141013173504.GA27955@redhat.com>
 <20141023183232.GW4977@linux.vnet.ibm.com>
 <20141023184018.GA12274@redhat.com>
 <20141023192807.GY4977@linux.vnet.ibm.com>
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On Thu, Oct 23, 2014 at 12:28:07PM -0700, Paul E. McKenney wrote:
 
 > >  > This one will require more looking.  But did you do something like
 > >  > create a pair of mutually recursive symlinks or something?  ;-)
 > > 
 > > I'm not 100% sure, but this may have been on a box that I was running
 > > tests on NFS. So maybe the server had disappeared with the mount
 > > still active..
 > > 
 > > Just a guess tbh.
 > 
 > Another possibility might be that the box was so overloaded that tasks
 > were getting preempted for 21 seconds as a matter of course, and sometimes
 > within RCU read-side critical sections.  Or did the box have ample idle
 > time?

I fairly recently upped the number of child processes I typically run
with, so it being overloaded does sound highly likely.

	Dave
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