Subject: random: Make it work on rt
From: Thomas Gleixner <tglx@linutronix.de>
Date: Tue, 21 Aug 2012 20:38:50 +0200
Origin: https://www.kernel.org/pub/linux/kernel/projects/rt/4.6/older/patches-4.6.2-rt5.tar.xz

Delegate the random insertion to the forced threaded interrupt
handler. Store the return IP of the hard interrupt handler in the irq
descriptor and feed it into the random generator as a source of
entropy.

Signed-off-by: Thomas Gleixner <tglx@linutronix.de>

---
 drivers/char/random.c   |   11 +++++------
 include/linux/irqdesc.h |    1 +
 include/linux/random.h  |    2 +-
 kernel/irq/handle.c     |    8 +++++++-
 kernel/irq/manage.c     |    6 ++++++
 5 files changed, 20 insertions(+), 8 deletions(-)

--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -888,28 +888,27 @@ static __u32 get_reg(struct fast_pool *f
 	return *(ptr + f->reg_idx++);
 }
 
-void add_interrupt_randomness(int irq, int irq_flags)
+void add_interrupt_randomness(int irq, int irq_flags, __u64 ip)
 {
 	struct entropy_store	*r;
 	struct fast_pool	*fast_pool = this_cpu_ptr(&irq_randomness);
-	struct pt_regs		*regs = get_irq_regs();
 	unsigned long		now = jiffies;
 	cycles_t		cycles = random_get_entropy();
 	__u32			c_high, j_high;
-	__u64			ip;
 	unsigned long		seed;
 	int			credit = 0;
 
 	if (cycles == 0)
-		cycles = get_reg(fast_pool, regs);
+		cycles = get_reg(fast_pool, NULL);
 	c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;
 	j_high = (sizeof(now) > 4) ? now >> 32 : 0;
 	fast_pool->pool[0] ^= cycles ^ j_high ^ irq;
 	fast_pool->pool[1] ^= now ^ c_high;
-	ip = regs ? instruction_pointer(regs) : _RET_IP_;
+	if (!ip)
+		ip = _RET_IP_;
 	fast_pool->pool[2] ^= ip;
 	fast_pool->pool[3] ^= (sizeof(ip) > 4) ? ip >> 32 :
-		get_reg(fast_pool, regs);
+		get_reg(fast_pool, NULL);
 
 	fast_mix(fast_pool);
 	add_interrupt_bench(cycles);
--- a/include/linux/irqdesc.h
+++ b/include/linux/irqdesc.h
@@ -64,6 +64,7 @@ struct irq_desc {
 	unsigned int		irqs_unhandled;
 	atomic_t		threads_handled;
 	int			threads_handled_last;
+	u64			random_ip;
 	raw_spinlock_t		lock;
 	struct cpumask		*percpu_enabled;
 #ifdef CONFIG_SMP
--- a/include/linux/random.h
+++ b/include/linux/random.h
@@ -20,7 +20,7 @@ struct random_ready_callback {
 extern void add_device_randomness(const void *, unsigned int);
 extern void add_input_randomness(unsigned int type, unsigned int code,
 				 unsigned int value);
-extern void add_interrupt_randomness(int irq, int irq_flags);
+extern void add_interrupt_randomness(int irq, int irq_flags, __u64 ip);
 
 extern void get_random_bytes(void *buf, int nbytes);
 extern int add_random_ready_callback(struct random_ready_callback *rdy);
--- a/kernel/irq/handle.c
+++ b/kernel/irq/handle.c
@@ -134,6 +134,8 @@ void __irq_wake_thread(struct irq_desc *
 
 irqreturn_t handle_irq_event_percpu(struct irq_desc *desc)
 {
+	struct pt_regs *regs = get_irq_regs();
+	u64 ip = regs ? instruction_pointer(regs) : 0;
 	irqreturn_t retval = IRQ_NONE;
 	unsigned int flags = 0, irq = desc->irq_data.irq;
 	struct irqaction *action;
@@ -174,7 +176,11 @@ irqreturn_t handle_irq_event_percpu(stru
 		retval |= res;
 	}
 
-	add_interrupt_randomness(irq, flags);
+#ifdef CONFIG_PREEMPT_RT_FULL
+	desc->random_ip = ip;
+#else
+	add_interrupt_randomness(irq, flags, ip);
+#endif
 
 	if (!noirqdebug)
 		note_interrupt(desc, retval);
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -1043,6 +1043,12 @@ static int irq_thread(void *data)
 		if (action_ret == IRQ_WAKE_THREAD)
 			irq_wake_secondary(desc, action);
 
+#ifdef CONFIG_PREEMPT_RT_FULL
+		migrate_disable();
+		add_interrupt_randomness(action->irq, 0,
+				 desc->random_ip ^ (unsigned long) action);
+		migrate_enable();
+#endif
 		wake_threads_waitq(desc);
 	}
 
