linux-kernel - [PATCH 3/5] random: Split add_interrupt

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Date:   Tue,  7 Dec 2021 13:17:35 +0100
From:   Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To:     linux-kernel@...r.kernel.org
Cc:     Theodore Ts'o <tytso@....edu>,
        "Jason A . Donenfeld " <Jason@...c4.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        Peter Zijlstra <peterz@...radead.org>,
        Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH 3/5] random: Split add_interrupt_randomness().

Split add_interrupt_randomness() into two parts:
- add_interrupt_randomness() which collects the entropy on the
  invocation of a hardware interrupt and it feeds into the fast_pool,
  a per-CPU variable (irq_randomness).

- process_interrupt_randomness_pool() which feeds the fast_pool/
  irq_randomness into the entropy_store if enough entropy has been
  gathered.

This is a preparations step to ease PREEMPT_RT support.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 drivers/char/random.c | 47 +++++++++++++++++++++++++------------------
 1 file changed, 27 insertions(+), 20 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index c8067c264a880..dfc38d87125f5 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1242,29 +1242,10 @@ static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
 	return *ptr;
 }
 
-void add_interrupt_randomness(int irq)
+static void process_interrupt_randomness_pool(struct fast_pool *fast_pool)
 {
 	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;
-
-	if (cycles == 0)
-		cycles = get_reg(fast_pool, regs);
-	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_;
-	fast_pool->pool[2] ^= ip;
-	fast_pool->pool[3] ^= (sizeof(ip) > 4) ? ip >> 32 :
-		get_reg(fast_pool, regs);
-
-	fast_mix(fast_pool);
-	add_interrupt_bench(cycles);
 
 	if (unlikely(crng_init == 0)) {
 		if ((fast_pool->count >= 64) &&
@@ -1293,6 +1274,32 @@ void add_interrupt_randomness(int irq)
 	/* award one bit for the contents of the fast pool */
 	credit_entropy_bits(r, 1);
 }
+
+void add_interrupt_randomness(int irq)
+{
+	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;
+
+	if (cycles == 0)
+		cycles = get_reg(fast_pool, regs);
+	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_;
+	fast_pool->pool[2] ^= ip;
+	fast_pool->pool[3] ^= (sizeof(ip) > 4) ? ip >> 32 :
+		get_reg(fast_pool, regs);
+
+	fast_mix(fast_pool);
+	add_interrupt_bench(cycles);
+
+	process_interrupt_randomness_pool(fast_pool);
+}
 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
 
 #ifdef CONFIG_BLOCK
-- 
2.34.1