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Commit 91fcb532 authored by Theodore Ts'o's avatar Theodore Ts'o
Browse files

random: always update the entropy pool under the spinlock 



Instead of using lockless techniques introduced in commit
902c098a, use spin_trylock to try to grab entropy pool's lock.  If
we can't get the lock, then just try again on the next interrupt.

Based on discussions with George Spelvin.

Signed-off-by: default avatarTheodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
parent 1795cd9b

drivers/char/random.c

+23 −21
Original line number Diff line number Diff line
@@ -495,9 +495,8 @@ static void _mix_pool_bytes(struct entropy_store *r, const void *in, 
	tap4 = r->poolinfo->tap4;

	tap5 = r->poolinfo->tap5;



	smp_rmb();

	input_rotate = ACCESS_ONCE(r->input_rotate);

	i = ACCESS_ONCE(r->add_ptr);

	input_rotate = r->input_rotate;

	i = r->add_ptr;



	/* mix one byte at a time to simplify size handling and churn faster */

	while (nbytes--) {
@@ -524,9 +523,8 @@ static void _mix_pool_bytes(struct entropy_store *r, const void *in, 
		input_rotate = (input_rotate + (i ? 7 : 14)) & 31;

	}



	ACCESS_ONCE(r->input_rotate) = input_rotate;

	ACCESS_ONCE(r->add_ptr) = i;

	smp_wmb();

	r->input_rotate = input_rotate;

	r->add_ptr = i;



	if (out)

		for (j = 0; j < 16; j++)
@@ -845,7 +843,7 @@ void add_interrupt_randomness(int irq, int irq_flags) 
	__u32			input[4], c_high, j_high;

	__u64			ip;

	unsigned long		seed;

	int			credit;

	int			credit = 0;



	c_high = (sizeof(cycles) > 4) ? cycles >> 32 : 0;

	j_high = (sizeof(now) > 4) ? now >> 32 : 0;
@@ -860,36 +858,40 @@ void add_interrupt_randomness(int irq, int irq_flags) 
	if ((fast_pool->count & 63) && !time_after(now, fast_pool->last + HZ))

		return;



	fast_pool->last = now;



	r = nonblocking_pool.initialized ? &input_pool : &nonblocking_pool;

	if (!spin_trylock(&r->lock)) {

		fast_pool->count--;

		return;

	}

	fast_pool->last = now;

	__mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);



	/*

	 * If we have architectural seed generator, produce a seed and

	 * add it to the pool.  For the sake of paranoia count it as

	 * 50% entropic.

	 */

	if (arch_get_random_seed_long(&seed)) {

		__mix_pool_bytes(r, &seed, sizeof(seed), NULL);

		credit += sizeof(seed) * 4;

	}

	spin_unlock(&r->lock);



	/*

	 * If we don't have a valid cycle counter, and we see

	 * back-to-back timer interrupts, then skip giving credit for

	 * any entropy, otherwise credit 1 bit.

	 */

	credit = 1;

	credit++;

	if (cycles == 0) {

		if (irq_flags & __IRQF_TIMER) {

			if (fast_pool->last_timer_intr)

				credit = 0;

				credit--;

			fast_pool->last_timer_intr = 1;

		} else

			fast_pool->last_timer_intr = 0;

	}



	/*

	 * If we have architectural seed generator, produce a seed and

	 * add it to the pool.  For the sake of paranoia count it as

	 * 50% entropic.

	 */

	if (arch_get_random_seed_long(&seed)) {

		__mix_pool_bytes(r, &seed, sizeof(seed), NULL);

		credit += sizeof(seed) * 4;

	}



	credit_entropy_bits(r, credit);

}