linux-kernel - [PATCH 4/5] random: Move the fast

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Date:   Tue,  7 Dec 2021 13:17:36 +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 4/5] random: Move the fast_pool reset into the caller.

The state of the fast_pool (number of added entropy, timestamp of last
addition) is reset after entropy has been consumed.

Move the reset of the fast_pool into the caller.
This is a preparations step to ease PREEMPT_RT support.

Signed-off-by: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
---
 drivers/char/random.c | 29 +++++++++++++++--------------
 1 file changed, 15 insertions(+), 14 deletions(-)

diff --git a/drivers/char/random.c b/drivers/char/random.c
index dfc38d87125f5..4bcaa7886201d 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -1242,37 +1242,35 @@ static __u32 get_reg(struct fast_pool *f, struct pt_regs *regs)
 	return *ptr;
 }
 
-static void process_interrupt_randomness_pool(struct fast_pool *fast_pool)
+static bool process_interrupt_randomness_pool(struct fast_pool *fast_pool)
 {
 	struct entropy_store	*r;
-	unsigned long		now = jiffies;
 
 	if (unlikely(crng_init == 0)) {
+		bool pool_reset = false;
+
 		if ((fast_pool->count >= 64) &&
 		    crng_fast_load((char *) fast_pool->pool,
-				   sizeof(fast_pool->pool))) {
-			fast_pool->count = 0;
-			fast_pool->last = now;
-		}
-		return;
+				   sizeof(fast_pool->pool)))
+			pool_reset = true;
+
+		return pool_reset;
 	}
 
 	if ((fast_pool->count < 64) &&
-	    !time_after(now, fast_pool->last + HZ))
-		return;
+	    !time_after(jiffies, fast_pool->last + HZ))
+		return false;
 
 	r = &input_pool;
 	if (!spin_trylock(&r->lock))
-		return;
+		return false;
 
-	fast_pool->last = now;
 	__mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool));
 	spin_unlock(&r->lock);
 
-	fast_pool->count = 0;
-
 	/* award one bit for the contents of the fast pool */
 	credit_entropy_bits(r, 1);
+	return true;
 }
 
 void add_interrupt_randomness(int irq)
@@ -1298,7 +1296,10 @@ void add_interrupt_randomness(int irq)
 	fast_mix(fast_pool);
 	add_interrupt_bench(cycles);
 
-	process_interrupt_randomness_pool(fast_pool);
+	if (process_interrupt_randomness_pool(fast_pool)) {
+		fast_pool->last = now;
+		fast_pool->count = 0;
+	}
 }
 EXPORT_SYMBOL_GPL(add_interrupt_randomness);
 
-- 
2.34.1