Re: [PATCH 1/2] PCI: Use local parameter pci_device_id for pci_get_subsys/class()

From: Feng Tang <feng.tang@intel.com>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: Yinghai Lu <yinghai@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
	Steven Rostedt <rostedt@goodmis.org>, Avi Kivity <avi@redhat.com>,
	Steven Rostedt <srostedt@redhat.com>,
	LKML <linux-kernel@vger.kernel.org>,
	"kvm@vger.kernel.org" <kvm@vger.kernel.org>,
	Kenji Kaneshige <kaneshige.kenji@jp.fujitsu.com>,
	<linux-pci@vger.kernel.org>, Bjorn Helgaas <bhelgaas@google.com>
Subject: Re: [PATCH 1/2] PCI: Use local parameter pci_device_id for pci_get_subsys/class()
Date: Sat, 8 Sep 2012 23:34:55 +0800	[thread overview]
Message-ID: <20120908233455.0d0527b3@feng-i7> (raw)
In-Reply-To: <20120908134220.GA24831@localhost>

On Sat, 8 Sep 2012 21:42:20 +0800
Fengguang Wu <fengguang.wu@intel.com> wrote:

> On Fri, Sep 07, 2012 at 06:32:48PM -0700, Yinghai Lu wrote:
> 
> > > with this one in pci/next pci config in /sys are not created.
> > >
> > > 10:~ # lspci -tv
> > > pcilib: Cannot open /sys/bus/pci/devices/0000:00:03.0/config
> > > lspci: Unable to read the standard configuration space header of
> > > device 0000:00:03.0
> > > pcilib: Cannot open /sys/bus/pci/devices/0000:00:02.0/config
> > > lspci: Unable to read the standard configuration space header of
> > > device 0000:00:02.0
> > > pcilib: Cannot open /sys/bus/pci/devices/0000:00:01.3/config
> > > lspci: Unable to read the standard configuration space header of
> > > device 0000:00:01.3
> > > pcilib: Cannot open /sys/bus/pci/devices/0000:00:01.1/config
> > > lspci: Unable to read the standard configuration space header of
> > > device 0000:00:01.1
> > > pcilib: Cannot open /sys/bus/pci/devices/0000:00:01.0/config
> > > lspci: Unable to read the standard configuration space header of
> > > device 0000:00:01.0
> > > pcilib: Cannot open /sys/bus/pci/devices/0000:00:00.0/config
> > > lspci: Unable to read the standard configuration space header of
> > > device 0000:00:00.0
> > > -[0000:00]-
> > >
> > > bisected to this commit
> > >
> > > ccee7d23102f5e5765ec24779c5b77472af8f79e is the first bad commit
> > > commit ccee7d23102f5e5765ec24779c5b77472af8f79e
> > > Author: Feng Tang <feng.tang@intel.com>
> > > Date:   Thu Aug 23 15:45:03 2012 +0800
> > >
> > >     PCI: Use pci_device_id on stack for pci_get_subsys/class() to avoid kmalloc
> > >
> > >     This fixes a kernel warning https://lkml.org/lkml/2012/7/31/682
> > >
> > >     pci_get_subsys() may get called in late system reboot stage, using
> > >     a sleepable kmalloc() sounds fragile and will cause a kernel warning
> > >     with my recent commmit 55c844a "x86/reboot: Fix a warning message
> > >     triggered by stop_other_cpus()" which disable local interrupt in
> > >     late system shutdown/reboot phase. Using a local parameter instead
> > >     will fix it and make it eligible for calling forom atomic context.
> > >
> > >     Do the same change for the pci_get_class() as suggested by Bjorn Helgaas
> > >
> > >     [bhelgaas: changelog]
> > >     Bisected-by: Fengguang Wu <fengguang.wu@intel.com>
> > >     Signed-off-by: Feng Tang <feng.tang@intel.com>
> > >     Signed-off-by: Bjorn Helgaas <bhelgaas@google.com>
> > >     Reviewed-by: Fengguang Wu <fengguang.wu@intel.com>
> > >
> > > :040000 040000 dee62a035816b73abc68e40de8f21c7349efc4cb
> > > 70b2a6258bffa1ab963bd650d8f5d02da774fbce M      drivers
> > >
> > > so the stack get overrun ?
> > >
> > > Bjorn, I think it is this one that cause lspci broken that I mentioned
> > > during meeting at San Diego.
> 
> This makes lspci work again on my side. The caveat is, kzalloc() will
> zero out all data while the new local variable leaves some data
> uninitialized.

Yes, thanks for the quick root cause and fix to the bug in my code.

- Feng