From: Paul Gortmaker <paul.gortmaker@windriver.com>
To: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-rt-users <linux-rt-users@vger.kernel.org>
Subject: Re: Crap, ksoftirqd/0 looping forever in softirq
Date: Thu, 11 Oct 2012 11:34:14 -0400 [thread overview]
Message-ID: <20121011153413.GB22583@windriver.com> (raw)
In-Reply-To: <20121011142130.GA22583@windriver.com>
[Re: Crap, ksoftirqd/0 looping forever in softirq] On 11/10/2012 (Thu 10:21) Paul Gortmaker wrote:
> [Crap, ksoftirqd/0 looping forever in softirq] On 10/10/2012 (Wed 20:16) Paul Gortmaker wrote:
>
> > Seeing the above message, I added a trivial change to print out the
> > Mask and Pending, and I consistently saw it was (both p/m) in every
> > case `was __IRQF_TIMER (0x200).
>
> Of cource it helps if I look up the value in the right list.
> I guess the ffs had me thinking "bits", instead of looking up
> the value in the softirq enum list.
>
> When I add a change to record the last vecs used and dump them
> out when the Crap message is triggered (using softirq_to_name
> instead of looking things up in random tables!) I get this:
>
> [ 20.887137] Crap, ksoftirqd/0 looping forever in softirq
> [ 20.887150] Last: RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU
> [ 20.920168] Crap, ksoftirqd/0 looping forever in softirq
> [ 20.920179] Last: RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU
> [ 20.954200] Crap, ksoftirqd/0 looping forever in softirq
> [ 20.954213] Last: RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU RCU
Here is a trace, which I think shows us that we call the
RCU softirq, which eventually calls invoke_rcu_core, which
is just "raise_softirq(RCU_SOFTIRQ);" so the loop which is
testing on current->softirqs_raised will never see it zero.
We clear it on entry with:
current->softirqs_raised &= ~mask;
but after we call:
do_single_softirq(i, need_rcu_bh_qs);
it will be re-armed by invoke_rcu_core.
0xffffffff81044d9d in __raise_softirq_irqoff (nr=9) at kernel/softirq.c:608
0xffffffff81044e29 in raise_softirq_irqoff (nr=<optimized out>) at kernel/softirq.c:618
0xffffffff810452e1 in raise_softirq (nr=<optimized out>) at kernel/softirq.c:744
0xffffffff810bd4e1 in invoke_rcu_core () at kernel/rcutree.c:1878
rcu_do_batch (rdp=0xffff880017c0bf80, rsp=<optimized out>) at kernel/rcutree.c:1635
invoke_rcu_callbacks (rdp=0xffff880017c0bf80, rsp=0xffffffff81c2b140) at kernel/rcutree.c:1870
__rcu_process_callbacks (rsp=0xffffffff81c2b140) at kernel/rcutree.c:1842
rcu_process_callbacks (unused=<optimized out>) at kernel/rcutree.c:1854
0xffffffff8104466b in handle_softirq (need_rcu_bh_qs=1, cpu=0, vec_nr=9) at kernel/softirq.c:149
do_single_softirq (need_rcu_bh_qs=1, which=9) at kernel/softirq.c:457
do_current_softirqs (need_rcu_bh_qs=1) at kernel/softirq.c:500
Does that sound right?
Paul.
next prev parent reply other threads:[~2012-10-11 15:34 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-10-11 0:16 Crap, ksoftirqd/0 looping forever in softirq Paul Gortmaker
2012-10-11 2:38 ` Mike Galbraith
2012-10-11 14:21 ` Paul Gortmaker
2012-10-11 15:34 ` Paul Gortmaker [this message]
2012-10-15 13:36 ` Paul E. McKenney
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