From: Thomas Gleixner <tglx@linutronix.de>
To: Boris Ostrovsky <boris.ostrovsky@oracle.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@kernel.org>,
Peter Zijlstra <peterz@infradead.org>,
Peter Anvin <hpa@zytor.com>, xiao jin <jin.xiao@intel.com>,
Joerg Roedel <jroedel@suse.de>, Borislav Petkov <bp@suse.de>,
Yanmin Zhang <yanmin_zhang@linux.intel.com>,
xen-devel <xen-devel@lists.xenproject.org>
Subject: Re: [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down
Date: Tue, 14 Jul 2015 19:32:02 +0200 (CEST) [thread overview]
Message-ID: <alpine.DEB.2.11.1507141901460.18576@nanos> (raw)
In-Reply-To: <55A532C2.4080306@oracle.com>
On Tue, 14 Jul 2015, Boris Ostrovsky wrote:
> On 07/14/2015 11:44 AM, Thomas Gleixner wrote:
> > On Tue, 14 Jul 2015, Boris Ostrovsky wrote:
> > > > Prevent allocation and freeing of interrupt descriptors accross cpu
> > > > hotplug.
> > >
> > > This breaks Xen guests that allocate interrupt descriptors in .cpu_up().
> > And where exactly does XEN allocate those descriptors?
>
> xen_cpu_up()
> xen_setup_timer()
> bind_virq_to_irqhandler()
> bind_virq_to_irq()
> xen_allocate_irq_dynamic()
> xen_allocate_irqs_dynamic()
> irq_alloc_descs()
>
>
> There is also a similar pass via xen_cpu_up() -> xen_smp_intr_init()
Sigh.
>
> >
> > > Any chance this locking can be moved into arch code?
> > No.
The issue here is that all architectures need that protection and just
Xen does irq allocations in cpu_up.
So moving that protection into architecture code is not really an
option.
> > > Otherwise we will need to have something like arch_post_cpu_up()
> > > after the lock is released.
I'm not sure, that this will work. You probably want to do this in the
cpu prepare stage, i.e. before calling __cpu_up().
I have to walk the dogs now. Will look into it later tonight.
> > > (The patch doesn't appear to have any side effects for the down path since
> > > Xen
> > > guests deallocate descriptors in __cpu_die()).
> > Exact place please.
>
> Whose place? Where descriptors are deallocated?
>
> __cpu_die()
> xen_cpu_die()
> xen_teardown_timer()
> unbind_from_irqhandler()
> unbind_from_irq()
> __unbind_from_irq()
> xen_free_irq()
> irq_free_descs()
> free_desc()
Right, that's outside the lock held region.
Thanks,
tglx
next prev parent reply other threads:[~2015-07-14 17:32 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-07-05 17:12 [patch 0/4] x86/irq: Plug a couple of cpu hotplug races Thomas Gleixner
2015-07-05 17:12 ` [patch 1/4] hotplug: Prevent alloc/free of irq descriptors during cpu up/down Thomas Gleixner
2015-07-07 9:48 ` [tip:irq/urgent] hotplug: Prevent alloc/ free " tip-bot for Thomas Gleixner
2015-07-07 20:06 ` tip-bot for Thomas Gleixner
2015-07-08 9:37 ` tip-bot for Thomas Gleixner
2015-07-14 14:39 ` [patch 1/4] hotplug: Prevent alloc/free " Boris Ostrovsky
2015-07-14 15:44 ` Thomas Gleixner
2015-07-14 16:03 ` Boris Ostrovsky
2015-07-14 17:32 ` Thomas Gleixner [this message]
2015-07-14 20:04 ` [Xen-devel] " Boris Ostrovsky
2015-07-14 20:15 ` Thomas Gleixner
2015-07-14 21:07 ` Boris Ostrovsky
2016-03-12 9:19 ` Thomas Gleixner
2016-03-14 13:12 ` Boris Ostrovsky
2015-07-05 17:12 ` [patch 2/4] x86: Plug irq vector hotplug race Thomas Gleixner
2015-07-07 9:57 ` [tip:x86/urgent] x86/irq: " tip-bot for Thomas Gleixner
2015-07-05 17:12 ` [patch 3/4] x86/irq: Use proper locking in check_irq_vectors_for_cpu_disable() Thomas Gleixner
2015-07-07 9:57 ` [tip:x86/urgent] " tip-bot for Thomas Gleixner
2015-07-05 17:12 ` [patch 4/4] x86/irq: Retrieve irq data after locking irq_desc Thomas Gleixner
2015-07-07 9:58 ` [tip:x86/urgent] " tip-bot for Thomas Gleixner
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