Re: [PATCH] PCI: dwc: fix MSI IRQ handler ordering

From: Stephen Warren <swarren@wwwdotorg.org>
To: Trent Piepho <tpiepho@impinj.com>,
	"jingoohan1@gmail.com" <jingoohan1@gmail.com>,
	"gustavo.pimentel@synopsys.com" <gustavo.pimentel@synopsys.com>
Cc: "jpinto@synopsys.com" <jpinto@synopsys.com>,
	"marex@denx.de" <marex@denx.de>,
	"shawn.guo@linaro.org" <shawn.guo@linaro.org>,
	"tharvey@gateworks.com" <tharvey@gateworks.com>,
	"lorenzo.pieralisi@arm.com" <lorenzo.pieralisi@arm.com>,
	"swarren@nvidia.com" <swarren@nvidia.com>,
	"m.mann@arkona-technologies.de" <m.mann@arkona-technologies.de>,
	"faiz_abbas@ti.com" <faiz_abbas@ti.com>,
	"xobs@kosagi.com" <xobs@kosagi.com>,
	"hrhaan@gmail.com" <hrhaan@gmail.com>,
	"jbe@pengutronix.de" <jbe@pengutronix.de>,
	"linux-pci@vger.kernel.org" <linux-pci@vger.kernel.org>,
	"bhelgaas@google.com" <bhelgaas@google.com>,
	"arnd@arndb.de" <arnd@arndb.de>
Subject: Re: [PATCH] PCI: dwc: fix MSI IRQ handler ordering
Date: Fri, 4 Jan 2019 16:00:46 -0700	[thread overview]
Message-ID: <1ff5138e-3de9-e7f9-38e6-feee4b8cefa7@wwwdotorg.org> (raw)
In-Reply-To: <1546641949.14247.20.camel@impinj.com>

On 1/4/19 3:45 PM, Trent Piepho wrote:
> On Fri, 2019-01-04 at 14:45 -0700, Stephen Warren wrote:
>> From: Stephen Warren <swarren@nvidia.com>
>>
>> The current code does this when handling MSI IRQs:
>>
>> a) Process the irq.
>> b) Clear the latched IRQ status.
>>
>> If a new IRQ occurs any time after (a) has read the IRQ status for the
>> last time and before (b), it will be lost. For example, this occurs in
> 
> There was a patch series to fix this bug, sent in October, stretching
> to December.
> 
> See "PCI: dwc: Fix interrupt race in when handling MSI"
> 
> And "PCI: designware: Move interrupt acking into the proper callback"
> 
> The result was more code changes, which in the end produce the same
> order of operations as is done here to fix the race.  But it uses the
> irq framework correctly.
> 
> I do not think this problem was introduced until 4.14, so the nvidia
> 4.9 must have additional patches if this is observed there.  I'm sure
> it was not present in 4.12, as we used that, and did not see the issue
> until updating to 4.16.

Yes, I took the DWC driver from our 4.14 kernel and dropped it into the 
4.9 kernel, so that's why the issue shows up in 4.9 for us.

> The current fix (for 4.21?) depends on significant restructuring that
> was done to this driver around 4.17, see "PCI: dwc: Move MSI IRQs
> allocation to IRQ domains hierarchical API".
> 
> I think my original patch ("Fix interrupt race ..") or your patch here,
> which is basically the same, should be ported to 4.14 stable.  But
> there are some other opinions on that.  It's not clear to me if the
> hierarchical domain stuff would be back ported to stable series.  It
> does not seem to me to be a good idea to do so.

Hmm. Well I guess I'll go for the patch I posted in our downstream 
kernels, since back-porting a bunch of not-yet-available restructuring 
to our ancient kernels doesn't sound pleasant:-) But I'll go and take a 
quick look at the other patches you mentioned just in case. Thanks!