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SubjectRe: [irqchip: irq/irqchip-next] irqdomain: Protect the linear revmap with RCU
On Mon, 05 Jul 2021 19:23:27 +0100,
Guenter Roeck <linux@roeck-us.net> wrote:
>
> Hi Marc,
>
> On 7/5/21 11:01 AM, Marc Zyngier wrote:
> > Hi Guenter,
> >
> > On Mon, 05 Jul 2021 18:23:52 +0100,
> > Guenter Roeck <linux@roeck-us.net> wrote:
> >>
> >> Hi,
> >>
> >> On Fri, Jun 11, 2021 at 01:54:36PM -0000, irqchip-bot for Marc Zyngier wrote:
> >>> The following commit has been merged into the irq/irqchip-next branch of irqchip:
> >>>
> >>> Commit-ID: d4a45c68dc81f9117ceaff9f058d5fae674181b9
> >>> Gitweb: https://git.kernel.org/pub/scm/linux/kernel/git/maz/arm-platforms/d4a45c68dc81f9117ceaff9f058d5fae674181b9
> >>> Author: Marc Zyngier <maz@kernel.org>
> >>> AuthorDate: Mon, 05 Apr 2021 12:57:27 +01:00
> >>> Committer: Marc Zyngier <maz@kernel.org>
> >>> CommitterDate: Thu, 10 Jun 2021 13:09:18 +01:00
> >>>
> >>> irqdomain: Protect the linear revmap with RCU
> >>>
> >>> It is pretty odd that the radix tree uses RCU while the linear
> >>> portion doesn't, leading to potential surprises for the users,
> >>> depending on how the irqdomain has been created.
> >>>
> >>> Fix this by moving the update of the linear revmap under
> >>> the mutex, and the lookup under the RCU read-side lock.
> >>>
> >>> The mutex name is updated to reflect that it doesn't only
> >>> cover the radix-tree anymore.
> >>>
> >>> Signed-off-by: Marc Zyngier <maz@kernel.org>
> >>
> >> This patch results in various RCU warnings when booting mipsel images
> >> in qemu. I can not revert the patch due to subsequent changes, so I
> >> don't know if a simple revert fixes the problem. Log messages and
> >> bisect log see below.
> >
> > Thanks for the heads up. Do you have a config file I can use to
> > reproduce this? The QEMU invocation runes would certainly help too.
> >
> > It strikes me that in drivers/irqchip/irq-mips-cpu.c,
> > plat_irq_dispatch() now uses the irqdomain resolution before
> > irq_enter() took place. That's certainly a latent bug. I'll fix that
> > regardless, but I'd like to make sure this is what you are seeing too.
> >
>
> See http://server.roeck-us.net/qemu/mipsel/
>
> config Complete configuration file
> defconfig Shortened configuration file
> rootfs.cpio root file system (initrd)
> run.sh qemu run script (tested with qemu 4.2.1 and 6.0.0)
> vmlinux Kernel image experiencing the problem (v5.13-9883-gaf9efb8b661)
>
> Hope this helps,

It definitely helps, and confirms my hunch. With the patch below, I'm
not getting the warnings anymore. I'm pretty sure a number of other
MIPS systems suffer from similar issues, which I'll address similarly.

Please let me know if that addresses the issue on your end.

Thanks,

M.

diff --git a/arch/mips/include/asm/irq.h b/arch/mips/include/asm/irq.h
index d1477ecb1af9..57561e0e6e8d 100644
--- a/arch/mips/include/asm/irq.h
+++ b/arch/mips/include/asm/irq.h
@@ -57,6 +57,9 @@ asmlinkage void plat_irq_dispatch(void);

extern void do_IRQ(unsigned int irq);

+struct irq_domain;
+extern void do_domain_IRQ(struct irq_domain *domain, unsigned int irq);
+
extern void arch_init_irq(void);
extern void spurious_interrupt(void);

diff --git a/arch/mips/kernel/irq.c b/arch/mips/kernel/irq.c
index 85b6c60f285d..c76005cd3b79 100644
--- a/arch/mips/kernel/irq.c
+++ b/arch/mips/kernel/irq.c
@@ -21,6 +21,7 @@
#include <linux/kallsyms.h>
#include <linux/kgdb.h>
#include <linux/ftrace.h>
+#include <linux/irqdomain.h>

#include <linux/atomic.h>
#include <linux/uaccess.h>
@@ -107,3 +108,16 @@ void __irq_entry do_IRQ(unsigned int irq)
irq_exit();
}

+void __irq_entry do_domain_IRQ(struct irq_domain *domain, unsigned int hwirq)
+{
+ struct irq_desc *desc;
+
+ irq_enter();
+ check_stack_overflow();
+
+ desc = irq_resolve_mapping(domain, hwirq);
+ if (likely(desc))
+ handle_irq_desc(desc);
+
+ irq_exit();
+}
diff --git a/drivers/irqchip/irq-mips-cpu.c b/drivers/irqchip/irq-mips-cpu.c
index 0bbb0b2d0dd5..0c7ae71a0af0 100644
--- a/drivers/irqchip/irq-mips-cpu.c
+++ b/drivers/irqchip/irq-mips-cpu.c
@@ -127,7 +127,6 @@ static struct irq_chip mips_mt_cpu_irq_controller = {
asmlinkage void __weak plat_irq_dispatch(void)
{
unsigned long pending = read_c0_cause() & read_c0_status() & ST0_IM;
- unsigned int virq;
int irq;

if (!pending) {
@@ -137,12 +136,15 @@ asmlinkage void __weak plat_irq_dispatch(void)

pending >>= CAUSEB_IP;
while (pending) {
+ struct irq_domain *d;
+
irq = fls(pending) - 1;
if (IS_ENABLED(CONFIG_GENERIC_IRQ_IPI) && irq < 2)
- virq = irq_linear_revmap(ipi_domain, irq);
+ d = ipi_domain;
else
- virq = irq_linear_revmap(irq_domain, irq);
- do_IRQ(virq);
+ d = irq_domain;
+
+ do_domain_IRQ(d, irq);
pending &= ~BIT(irq);
}
}
--
Without deviation from the norm, progress is not possible.

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