RE: [patch 25/26] x86: hyperv: Cleanup the irq mess

[Thomas Gleixner <tglx@linutronix.de>]

On Tue, 25 Feb 2014, KY Srinivasan wrote:
> > -----Original Message-----
> > From: Thomas Gleixner [mailto:tglx@linutronix.de]
> > Sent: Sunday, February 23, 2014 1:40 PM
> > To: LKML
> > Cc: Ingo Molnar; Peter Zijlstra; x86; KY Srinivasan; Greg Kroah-Hartman;
> > linuxdrivers
> > Subject: [patch 25/26] x86: hyperv: Cleanup the irq mess
> > 
> > The vmbus/hyperv interrupt handling is another complete trainwreck and
> > probably the worst of all currently in tree.
> > 
> > If CONFIG_HYPERV=y then the interrupt delivery to the vmbus happens via
> > the direct HYPERVISOR_CALLBACK_VECTOR. So far so good, but:
> > 
> >   The driver requests first a normal device interrupt. The only reason
> >   to do so is to increment the interrupt stats of that device
> >   interrupt.
> > 
> >   We have proper accounting mechanisms for direct vectors, but of
> >   course it's too much effort to add that 5 lines of code.
> > 
> >   Aside of that the alloc_intr_gate() is not protected against
> >   reallocation which makes module reload impossible.
> > 
> > If CONFIG_HYPERV=n then the vmbus request a regular device interrupt via
> > request_irq() and installs it's own private flow handler. Of course this lacks
> > any explanation why it can't use the standard flow handler or the existing
> > handle_percpu_irq handler.
> > 
> > Solution to the problem is simple to rip out the whole mess and implement it
> > correctly.
> Thomas,
> 
> Thank you for cleaning up this code. When CONFIG_HYPERV== n, none of
> the VMBUS code is active.  The special case can go away as you have
> noted.

So, if CONFIG_HYPERV=n then you do not need the request_irq() fallback
at all, right? Somehow I missed the HYPERV dependency of the VMBUS stuff

That makes stuff even simpler as we can get rid of those extra cases
including the extra flow handler.

New patch below.

Thanks,

	tglx
---

 arch/x86/include/asm/mshyperv.h |    4 +-
 arch/x86/kernel/cpu/mshyperv.c  |   78 ++++++++++++++++++++--------------------
 drivers/hv/vmbus_drv.c          |   39 ++------------------
 3 files changed, 47 insertions(+), 74 deletions(-)

Index: tip/arch/x86/include/asm/mshyperv.h
===================================================================
--- tip.orig/arch/x86/include/asm/mshyperv.h
+++ tip/arch/x86/include/asm/mshyperv.h
@@ -2,6 +2,7 @@
 #define _ASM_X86_MSHYPER_H
 
 #include <linux/types.h>
+#include <linux/interrupt.h>
 #include <asm/hyperv.h>
 
 struct ms_hyperv_info {
@@ -16,6 +17,7 @@ void hyperv_callback_vector(void);
 #define trace_hyperv_callback_vector hyperv_callback_vector
 #endif
 void hyperv_vector_handler(struct pt_regs *regs);
-void hv_register_vmbus_handler(int irq, irq_handler_t handler);
+int hv_setup_vmbus_irq(int irq, irq_handler_t handler, void *dev_id);
+void hv_remove_vmbus_irq(int irq, void *dev_id);
 
 #endif
Index: tip/arch/x86/kernel/cpu/mshyperv.c
===================================================================
--- tip.orig/arch/x86/kernel/cpu/mshyperv.c
+++ tip/arch/x86/kernel/cpu/mshyperv.c
@@ -17,6 +17,7 @@
 #include <linux/hardirq.h>
 #include <linux/efi.h>
 #include <linux/interrupt.h>
+#include <linux/irq.h>
 #include <asm/processor.h>
 #include <asm/hypervisor.h>
 #include <asm/hyperv.h>
@@ -30,6 +31,45 @@
 struct ms_hyperv_info ms_hyperv;
 EXPORT_SYMBOL_GPL(ms_hyperv);
 
+#ifdef CONFIG_HYPERV
+static irq_handler_t *vmbus_handler;
+
+void hyperv_vector_handler(struct pt_regs *regs)
+{
+	struct pt_regs *old_regs = set_irq_regs(regs);
+
+	irq_enter();
+	exit_idle();
+
+	inc_irq_stat(irq_hv_callback_count);
+	if (vmbus_handler)
+		vmbus_handler();
+
+	irq_exit();
+	set_irq_regs(old_regs);
+}
+
+int hv_setup_vmbus_irq(int irq, irq_handler_t *handler, void *dev_id)
+{
+	vmbus_handler = handler;
+	/*
+	 * Setup the IDT for hypervisor callback. Prevent reallocation
+	 * at module reload.
+	 */
+	if (!test_bit(HYPERVISOR_CALLBACK_VECTOR, used_vectors))
+		alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR,
+				hyperv_callback_vector);
+}
+
+void hv_remove_vmbus_irq(unsigned int irq, void *dev_id)
+{
+	/* We have no way to deallocate the interrupt gate */
+	vmbus_handler = NULL;
+}
+EXPORT_SYMBOL_GPL(hv_setup_vmbus_irq);
+EXPORT_SYMBOL_GPL(hv_remove_vmbus_irq);
+#endif
+
 static uint32_t  __init ms_hyperv_platform(void)
 {
 	u32 eax;
@@ -113,41 +153,3 @@ const __refconst struct hypervisor_x86 x
 	.init_platform		= ms_hyperv_init_platform,
 };
 EXPORT_SYMBOL(x86_hyper_ms_hyperv);
-
-#if IS_ENABLED(CONFIG_HYPERV)
-static int vmbus_irq = -1;
-static irq_handler_t vmbus_isr;
-
-void hv_register_vmbus_handler(int irq, irq_handler_t handler)
-{
-	/*
-	 * Setup the IDT for hypervisor callback.
-	 */
-	alloc_intr_gate(HYPERVISOR_CALLBACK_VECTOR, hyperv_callback_vector);
-
-	vmbus_irq = irq;
-	vmbus_isr = handler;
-}
-
-void hyperv_vector_handler(struct pt_regs *regs)
-{
-	struct pt_regs *old_regs = set_irq_regs(regs);
-	struct irq_desc *desc;
-
-	irq_enter();
-	exit_idle();
-
-	desc = irq_to_desc(vmbus_irq);
-
-	if (desc)
-		generic_handle_irq_desc(vmbus_irq, desc);
-
-	irq_exit();
-	set_irq_regs(old_regs);
-}
-#else
-void hv_register_vmbus_handler(int irq, irq_handler_t handler)
-{
-}
-#endif
-EXPORT_SYMBOL_GPL(hv_register_vmbus_handler);
Index: tip/drivers/hv/vmbus_drv.c
===================================================================
--- tip.orig/drivers/hv/vmbus_drv.c
+++ tip/drivers/hv/vmbus_drv.c
@@ -25,7 +25,6 @@
 #include <linux/init.h>
 #include <linux/module.h>
 #include <linux/device.h>
-#include <linux/irq.h>
 #include <linux/interrupt.h>
 #include <linux/sysctl.h>
 #include <linux/slab.h>
@@ -558,9 +557,6 @@ static struct bus_type  hv_bus = {
 	.dev_groups =		vmbus_groups,
 };
 
-static const char *driver_name = "hyperv";
-
-
 struct onmessage_work_context {
 	struct work_struct work;
 	struct hv_message msg;
@@ -677,19 +673,6 @@ static irqreturn_t vmbus_isr(int irq, vo
 }
 
 /*
- * vmbus interrupt flow handler:
- * vmbus interrupts can concurrently occur on multiple CPUs and
- * can be handled concurrently.
- */
-
-static void vmbus_flow_handler(unsigned int irq, struct irq_desc *desc)
-{
-	kstat_incr_irqs_this_cpu(irq, desc);
-
-	desc->action->handler(irq, desc->action->dev_id);
-}
-
-/*
  * vmbus_bus_init -Main vmbus driver initialization routine.
  *
  * Here, we
@@ -715,26 +698,13 @@ static int vmbus_bus_init(int irq)
 	if (ret)
 		goto err_cleanup;
 
-	ret = request_irq(irq, vmbus_isr, 0, driver_name, hv_acpi_dev);
+	ret = hv_setup_vmbus_irq(irq, vmbus_isr, hv_acpi_dev);
 
 	if (ret != 0) {
-		pr_err("Unable to request IRQ %d\n",
-			   irq);
+		pr_err("Unable to request IRQ %d\n", irq);
 		goto err_unregister;
 	}
 
-	/*
-	 * Vmbus interrupts can be handled concurrently on
-	 * different CPUs. Establish an appropriate interrupt flow
-	 * handler that can support this model.
-	 */
-	irq_set_handler(irq, vmbus_flow_handler);
-
-	/*
-	 * Register our interrupt handler.
-	 */
-	hv_register_vmbus_handler(irq, vmbus_isr);
-
 	ret = hv_synic_alloc();
 	if (ret)
 		goto err_alloc;
@@ -753,7 +723,7 @@ static int vmbus_bus_init(int irq)
 
 err_alloc:
 	hv_synic_free();
-	free_irq(irq, hv_acpi_dev);
+	hv_remove_vmbus_irq(irq, hv_acpi_dev);
 
 err_unregister:
 	bus_unregister(&hv_bus);
@@ -978,8 +948,7 @@ cleanup:
 
 static void __exit vmbus_exit(void)
 {
-
-	free_irq(irq, hv_acpi_dev);
+	hv_remove_vmbus_irq(irq, hv_acpi_dev);
 	vmbus_free_channels();
 	bus_unregister(&hv_bus);
 	hv_cleanup();