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From: Peter Zijlstra <peterz@infradead.org>
To: Sasha Levin <sasha.levin@oracle.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Dave Jones <davej@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: sched: long running interrupts breaking spinlocks
Date: Tue, 8 Apr 2014 18:10:23 +0200	[thread overview]
Message-ID: <20140408161023.GP10526@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <53441540.7070102@oracle.com>

On Tue, Apr 08, 2014 at 11:26:56AM -0400, Sasha Levin wrote:
> Hi all,
> 
> (all the below happened inside mm/ code, so while I don't suspect
> it's a mm/ issue you folks got cc'ed anyways!)
> 
> While fuzzing with trinity inside a KVM tools guest running the latest -next
> kernel, I've stumbled on the following:
> 
> [ 4071.166362] BUG: spinlock lockup suspected on CPU#19, trinity-c19/17092

That's a heuristic in the spinlock code; triggering it with big machines
(19 cpus is far bigger than anything at the time that code was written)
and virt (yay for lock owner preemption; another thing we didn't have
back when) is trivial.

I'd not worry too much about this.

So DEBUG_SPINLOCKS turns spin_lock() into something like:

  for (i = 0; i < loops; i++)
  	if (spin_trylock())
		return;

  /* complain */

And you simply ran out of loops.

--
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WARNING: multiple messages have this Message-ID (diff)
From: Peter Zijlstra <peterz@infradead.org>
To: Sasha Levin <sasha.levin@oracle.com>
Cc: Ingo Molnar <mingo@kernel.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	"linux-mm@kvack.org" <linux-mm@kvack.org>,
	LKML <linux-kernel@vger.kernel.org>,
	Dave Jones <davej@redhat.com>,
	Thomas Gleixner <tglx@linutronix.de>
Subject: Re: sched: long running interrupts breaking spinlocks
Date: Tue, 8 Apr 2014 18:10:23 +0200	[thread overview]
Message-ID: <20140408161023.GP10526@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <53441540.7070102@oracle.com>

On Tue, Apr 08, 2014 at 11:26:56AM -0400, Sasha Levin wrote:
> Hi all,
> 
> (all the below happened inside mm/ code, so while I don't suspect
> it's a mm/ issue you folks got cc'ed anyways!)
> 
> While fuzzing with trinity inside a KVM tools guest running the latest -next
> kernel, I've stumbled on the following:
> 
> [ 4071.166362] BUG: spinlock lockup suspected on CPU#19, trinity-c19/17092

That's a heuristic in the spinlock code; triggering it with big machines
(19 cpus is far bigger than anything at the time that code was written)
and virt (yay for lock owner preemption; another thing we didn't have
back when) is trivial.

I'd not worry too much about this.

So DEBUG_SPINLOCKS turns spin_lock() into something like:

  for (i = 0; i < loops; i++)
  	if (spin_trylock())
		return;

  /* complain */

And you simply ran out of loops.

  reply	other threads:[~2014-04-08 16:10 UTC|newest]

Thread overview: 4+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2014-04-08 15:26 sched: long running interrupts breaking spinlocks Sasha Levin
2014-04-08 15:26 ` Sasha Levin
2014-04-08 16:10 ` Peter Zijlstra [this message]
2014-04-08 16:10   ` Peter Zijlstra

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