random: always update the entropy pool under the spinlock
Instead of using lockless techniques introduced in commit
902c098a3663, 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: Theodore Ts'o <tytso@mit.edu>
Cc: George Spelvin <linux@horizon.com>
diff --git a/drivers/char/random.c b/drivers/char/random.c
index 0a7ac0a..922a2e4 100644
--- a/drivers/char/random.c
+++ b/drivers/char/random.c
@@ -495,9 +495,8 @@
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 @@
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 @@
__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;
@@ -860,25 +858,13 @@
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;
- __mix_pool_bytes(r, &fast_pool->pool, sizeof(fast_pool->pool), NULL);
-
- /*
- * 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;
- if (cycles == 0) {
- if (irq_flags & __IRQF_TIMER) {
- if (fast_pool->last_timer_intr)
- credit = 0;
- fast_pool->last_timer_intr = 1;
- } else
- fast_pool->last_timer_intr = 0;
+ 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
@@ -889,6 +875,22 @@
__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++;
+ if (cycles == 0) {
+ if (irq_flags & __IRQF_TIMER) {
+ if (fast_pool->last_timer_intr)
+ credit--;
+ fast_pool->last_timer_intr = 1;
+ } else
+ fast_pool->last_timer_intr = 0;
+ }
credit_entropy_bits(r, credit);
}