On Wed, 2009-04-22 at 14:26 +0200, Jan Kiszka wrote:
> Hi all,
> issuing  rtdm_irq_request and, thus, xnintr_attach can trigger a
> "I-pipe: Detected stalled topmost domain, probably caused by a bug." if
> the interrupt type is MSI:
>   [<ffffffff80273cce>] ipipe_check_context+0xe7/0xe9
>   [<ffffffff8049dae9>] _spin_lock_irqsave+0x18/0x54
>   [<ffffffff8037dcc2>] pci_bus_read_config_dword+0x3c/0x87
>   [<ffffffff80387c1d>] read_msi_msg+0x61/0xe1
>   [<ffffffff8021c5b8>] ? assign_irq_vector+0x3e/0x49
>   [<ffffffff8021d7b2>] set_msi_irq_affinity+0x6d/0xc8
>   [<ffffffff8021fa5d>] __ipipe_set_irq_affinity+0x6c/0x77
>   [<ffffffff80274231>] ipipe_set_irq_affinity+0x34/0x3d
>   [<ffffffff8027c572>] xnintr_attach+0xaa/0x11e
> Two option to fix this, but I'm currently undecided which one to go:
>  - harden pci_lock (drivers/pci/access.c) - didn't we applied such a
>    MSI-related workaround before?

This did not work as expected: pathological latency spots. This said,
the vanilla code has evolved since I tried this quick hack months ago,
so it may be worth to look at this option once again.

>  - move xnarch_set_irq_affinity out of intrlock (but couldn't we face
>    even more pci_lock related issues?)

Since upstream decided to use PCI config reads even inside hot paths
when processing MSI interrupts, the only sane way would be to make the
locking used there Adeos-aware, likely virtualizing the interrupt mask.
The way upstream generally deals with MSI is currently a problem for us.

> Jan

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