linux-kernel - Re: [BUG] lockdep splat with cpu_hotplug

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Date:   Fri, 21 Jul 2017 11:42:05 +0200 (CEST)
From:   Thomas Gleixner <tglx@...utronix.de>
To:     James Bottomley <James.Bottomley@...senPartnership.com>
cc:     Steven Rostedt <rostedt@...dmis.org>,
        LKML <linux-kernel@...r.kernel.org>,
        linux-scsi <linux-scsi@...r.kernel.org>,
        QLogic-Storage-Upstream@...gic.com, martin.petersen@...cle.com
Subject: Re: [BUG] lockdep splat with cpu_hotplug_lock

On Thu, 20 Jul 2017, James Bottomley wrote:
> [redirecting to linux-scsi]
> On Thu, 2017-07-20 at 19:35 -0400, Steven Rostedt wrote:
> > My tests triggered this splat on 4.13-rc1:
> > 
> > Loading iSCSI transport class v2.0-870.
> > QLogic NetXtreme II iSCSI Driver bnx2i v2.7.10.1 (Jul 16, 2014)
> > iscsi: registered transport (bnx2i)
> > 
> > ============================================
> > WARNING: possible recursive locking detected
> > 4.13.0-rc1-test+ #2 Not tainted
> > --------------------------------------------
> > swapper/0/1 is trying to acquire lock:
> >  (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffffb505329e>]
> > __cpuhp_setup_state+0x28/0x59
> > 
> > but task is already holding lock:
> >  (cpu_hotplug_lock.rw_sem){++++++}, at: [<ffffffffb64d54e9>]
> > bnx2i_mod_init+0x134/0x209
> > 
> > other info that might help us debug this:
> >  Possible unsafe locking scenario:
> > 
> >        CPU0
> >        ----
> >   lock(cpu_hotplug_lock.rw_sem);
> >   lock(cpu_hotplug_lock.rw_sem);
> 
> It sounds like it's an annotation issue not an actual problem.  I've
> added the correct list, so hopefully our usual enthusiasts can take a
> look.

Nope. It's a recursive locking/\ of cpuhotplug lock. I'll have a look on
monday.

Thanks,

	tglx