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[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [win-pv-devel] Advice on evtchn interrupt handling
On 2015-12-09 11:44, Paul Durrant wrote: >> -----Original Message----- >> From: win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx [mailto:win-pv-devel- >> bounces@xxxxxxxxxxxxxxxxxxxx] On Behalf Of Rafal Wojdyla >> Sent: 09 December 2015 10:19 >> To: win-pv-devel@xxxxxxxxxxxxxxxxxxxx >> Subject: [win-pv-devel] Advice on evtchn interrupt handling >> >> Hi, >> >> I found an issue in my evtchn handling in xeniface that I'm not sure how >> to properly fix. Namely, the interrupt callback that's assigned for a >> particular channel can be called before its queued DPC (that signals the >> caller-provided event) finishes. In such case the interrupt callback >> fails to insert the DPC again and an event is lost, potentially causing >> a vchan "deadlock" down the way. >> > > Hi Rafal, > > That shouldn't be the case. Windows de-queues a DPC before running for > precisely this kind of reason. I.e. just because your DPC is running, it > should not stop another from being queued. Are you definitely seeing a > failure to queue even when no DPC is actually queued? What you may actually > be getting caught by is evtchn auto-masking. If you have enabled auto-masking > then you need to explicitly unmask at the end of your DPC. (The transmitter > and receiver ring DPCs in XENVIF are a good example of this). > > Cheers, > > Paul > Here's the relevant bit: http://xenbits.xen.org/gitweb/?p=pvdrivers/win/xeniface.git;a=blob;f=src/xeniface/ioctl_evtchn.c;h=9c5af19e00a91a08f68da0c630709cbaa6e8413d;hb=HEAD#l66 I check the result of KeInsertQueueDpc() and I definitely see it fail sometimes, even if the HVM only has 1 vcpu. My DPC unmasks the channel after setting an event so this shouldn't be the reason. >> Any advice on how to approach this? The interrupt callback runs at >> HIGH_LEVEL which is an issue when it comes to synchronization with some >> other code that could take care of such "pending" events. >> >> Also I wonder if the kernel differentiates DPCs only by their KDPC >> address, or also by arguments passed to KeInsertQueueDpc()? >> -- RafaÅ WojdyÅa Qubes Tools for Windows developer https://www.qubes-os.org/ _______________________________________________ win-pv-devel mailing list win-pv-devel@xxxxxxxxxxxxxxxxxxxx http://lists.xenproject.org/cgi-bin/mailman/listinfo/win-pv-devel
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