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RE: [PATCH] Fix div by zero in xenvif if no queues.
- To: "paul@xxxxxxx" <paul@xxxxxxx>, "win-pv-devel@xxxxxxxxxxxxxxxxxxxx" <win-pv-devel@xxxxxxxxxxxxxxxxxxxx>
- From: Martin Harvey <martin.harvey@xxxxxxxxxx>
- Date: Mon, 21 Mar 2022 16:18:52 +0000
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- Thread-topic: [PATCH] Fix div by zero in xenvif if no queues.
-----Original Message-----
From: win-pv-devel <win-pv-devel-bounces@xxxxxxxxxxxxxxxxxxxx> On Behalf Of
Durrant, Paul
> There is locking that is supposed to stop that from happening.
> VifTransmitterQueuePacketVersion() calls AcquireMrswLockShared() to make sure
> that state is not changing underneath it.
Ah, yes, I see what you mean. The various frontend state changes are meant to
be synchronised under the VIF lock. (However I note that we may not be the only
VIF ....). And then there's a little bit of extra sync to do with the suspend /
resume early/late callbacks.
> It really should not happen at all.
OK. I'll look back through the logs a bit more carefully. I suspect that after
resuming from suspend, the frontend state is getting set to UNKNOWN outside the
VIF Mrsw lock. Possible candidates I shall take a look at:
1. VIF mrsw lock not correctly shared between all users of frontend state.
2. Any frontend state changes commanded by VBD? (Not looked yet).
3. Some error path which bypasses the VIF lock.
4. Some corner case / race condition with early/late suspend callbacks.
5. Changes to the frontend state commanded by other power callbacks which have
bypassed the VIF lock.
Those are all the potential holes I can think of off the top of my head ...
MH.
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