On Tue, 2015-04-28 at 18:08 +0100, Marc Zyngier wrote: > On 28/04/15 17:51, Mark Salter wrote: > > If there are devices sharing an interrupt, acpi_register_gsi() could > > be called multiple times for the same gsi. Currently, it just maps > > the gsi without checking for a previous mapping. This patch adds a > > check for an existing mapping and uses that if found. > > > > Cc: Hanjun Guo <hanjun.guo@xxxxxxxxxx> > > Cc: Marc Zyngier <marc.zyngier@xxxxxxx> > > Cc: Lorenzo Pieralisi <lorenzo.pieralisi@xxxxxxx> > > Cc: Will Deacon <will.deacon@xxxxxxx> > > Signed-off-by: Mark Salter <msalter@xxxxxxxxxx> > > --- > > drivers/acpi/gsi.c | 7 +++++++ > > 1 file changed, 7 insertions(+) > > > > diff --git a/drivers/acpi/gsi.c b/drivers/acpi/gsi.c > > index 38208f2..5698c4f 100644 > > --- a/drivers/acpi/gsi.c > > +++ b/drivers/acpi/gsi.c > > @@ -76,6 +76,13 @@ int acpi_register_gsi(struct device *dev, u32 gsi, int trigger, > > unsigned int irq_type = acpi_gsi_get_irq_type(trigger, polarity); > > > > /* > > + * The gsi may be shared with other devices, so check for a > > + * previous mapping and use that if found. > > + */ > > + if (acpi_gsi_to_irq(gsi, &irq) > 0) > > + return irq; > > I'm afraid that's completely racy, and doesn't prevent much (two CPUs > can execute this at the same time and still end up executing the rest of > the code). > > Furthermore, irq_create_mapping is *designed* to handle that situation, You're right. irq_create_mapping does that check already. But if it is truly racy, irq_create_mapping has the same problem. > and returns the same virtual IRQ for a given hwirq (and it has the > proper locking...). > > So maybe it would be worth explaining the actual problem you're seeing, > because the code as it stands should handle the problem you seem to > describe. Sorry for the noise. I was experimenting with some other code in acpi_register_gsi which called __irq_domain_alloc_irqs directly which bypassed the check in irq_create_mapping. And that turns out to be a silly thing to do anyway, so nevermind. -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
