Re: [PATCH] PCI: altera-msi: Remove irq handler and data in one go

[Martin Kaiser]

Thus wrote Bjorn Helgaas (helgaas@xxxxxxxxxx):

> [+cc Florian, sorry, I hadn't seen your ack when I sent the below]

> On Tue, Nov 10, 2020 at 03:21:36PM -0600, Bjorn Helgaas wrote:
> > [+cc Nicolas, Jingoo, Gustavo, Toan]

> > On Sun, Nov 08, 2020 at 08:11:40PM +0100, Martin Kaiser wrote:
> > > Replace the two separate calls for removing the irq handler and data with a
> > > single irq_set_chained_handler_and_data() call.

> > This is similar to these:

> >   36f024ed8fc9 ("PCI/MSI: pci-xgene-msi: Consolidate chained IRQ handler install/remove")
> >   5168a73ce32d ("PCI/keystone: Consolidate chained IRQ handler install/remove")
> >   2cf5a03cb29d ("PCI/keystone: Fix race in installing chained IRQ handler")

> > and it seems potentially important that this removes the IRQ handler
> > and data *atomically*, i.e., both are done while holding
> > irq_get_desc_buslock().  

Ok, understood.

> > So I would use this:

> >   PCI: altera-msi: Fix race in installing chained IRQ handler

> >   Fix a race where a pending interrupt could be received and the handler
> >   called before the handler's data has been setup by converting to
> >   irq_set_chained_handler_and_data().

> >   See also 2cf5a03cb29d ("PCI/keystone: Fix race in installing chained
> >   IRQ handler").

> > to make it clear that this is actually a bug fix, not just a cleanup.

Thomas' commit 2cf5a03cb29d fixed a case where the handler was installed.
We're removing the handler here so his commit message doesn't really fit.
Anyway, I'll rewrite the commit message to clarify that this fixes a
race condition.

> > Looks like this should also be done in dw_pcie_free_msi() and

I'll send a patch for this.

> > xgene_msi_hwirq_alloc() at the same time?

This function uses the error status from irq_set_handler_data().
irq_set_chained_handler_and_data() returns no such error status. Is it
ok to drop the error handling?

Thanks,
Martin