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From: Keith Busch <keith.busch@intel.com>
To: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Cc: Bjorn Helgaas <helgaas@kernel.org>,
	Alexandru Gagniuc <mr.nuke.me@gmail.com>,
	linux-pci@vger.kernel.org, alex_gagniuc@dellteam.com,
	austin_bolen@dell.com, shyam_iyer@dell.com,
	linux-kernel@vger.kernel.org,
	Jonathan Derrick <jonathan.derrick@intel.com>,
	Lukas Wunner <lukas@wunner.de>,
	Russell Currey <ruscur@russell.cc>,
	Sam Bobroff <sbobroff@linux.ibm.com>,
	Oliver O'Halloran <oohall@gmail.com>,
	linuxppc-dev@lists.ozlabs.org
Subject: Re: [PATCH v2] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected
Date: Thu, 8 Nov 2018 15:32:58 -0700	[thread overview]
Message-ID: <20181108223258.GD2932@localhost.localdomain> (raw)
In-Reply-To: <20181108220117.GA11466@kroah.com>

On Thu, Nov 08, 2018 at 02:01:17PM -0800, Greg Kroah-Hartman wrote:
> On Thu, Nov 08, 2018 at 02:09:17PM -0600, Bjorn Helgaas wrote:
> > I'm having second thoughts about this.  One thing I'm uncomfortable
> > with is that sprinkling pci_dev_is_disconnected() around feels ad hoc
> > instead of systematic, in the sense that I don't know how we convince
> > ourselves that this (and only this) is the correct place to put it.
> 
> I think my stance always has been that this call is not good at all
> because once you call it you never really know if it is still true as
> the device could have been removed right afterward.
> 
> So almost any code that relies on it is broken, there is no locking and
> it can and will race and you will loose.

AIUI, we're not trying to create code to rely on this. This more about
reducing reliance on hardware. If the software misses the race once and
accesses disconnected device memory, that's usually not a big deal to
let hardware sort it out, but the point is not to push our luck.

Surprise hot remove is empirically more reliable the less we interact
with hardware and firmware. That shouldn't be necessary, but is just an
unfortunate reality.

  reply	other threads:[~2018-11-08 22:36 UTC|newest]

Thread overview: 34+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-09-18 22:15 [PATCH v2] PCI/MSI: Don't touch MSI bits when the PCI device is disconnected Alexandru Gagniuc
2018-11-06  0:32 ` Alex G.
2018-11-07 17:04   ` Derrick, Jonathan
2018-11-07 23:42 ` Bjorn Helgaas
2018-11-08 20:09   ` Bjorn Helgaas
2018-11-08 21:49     ` Keith Busch
2018-11-08 22:01     ` Greg Kroah-Hartman
2018-11-08 22:32       ` Keith Busch [this message]
2018-11-08 22:42         ` Greg Kroah-Hartman
2018-11-08 22:49           ` Alex_Gagniuc
2018-11-08 22:51             ` Greg KH
2018-11-08 23:06               ` Alex_Gagniuc
2018-11-12  5:49                 ` Oliver O'Halloran
2018-11-12 20:05                   ` Alex_Gagniuc
2018-11-13  5:02                     ` Bjorn Helgaas
2018-11-13 22:39                       ` Alex_Gagniuc
2018-11-13 22:52                         ` Keith Busch
2018-11-14  0:31                           ` Alex_Gagniuc
2018-11-14  5:59                         ` Bjorn Helgaas
2018-11-14 19:22                           ` Alex_Gagniuc
2018-11-14 19:41                             ` Derrick, Jonathan
2018-11-14 20:23                             ` Keith Busch
2018-11-14 20:52                               ` Alex_Gagniuc
2018-11-14 20:58                                 ` Keith Busch
2018-11-15  6:24                             ` Bjorn Helgaas
2018-11-16  0:19                               ` Alex_Gagniuc
2018-11-08 23:03           ` Keith Busch
2018-11-09  7:29       ` Lukas Wunner
2018-11-09 11:32         ` Greg Kroah-Hartman
2018-11-09 16:36           ` Keith Busch
2018-11-08 22:20     ` Alex_Gagniuc
2018-11-09  7:11     ` Lukas Wunner
2018-11-12  5:48       ` Oliver O'Halloran
2018-12-27 19:28     ` Alex_Gagniuc

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