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random: always update the entropy pool under the spinlock

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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>
This commit is contained in:
Theodore Ts'o 2014-06-10 22:46:37 -04:00
parent 1795cd9b3a
commit 91fcb532ef
1 changed files with 26 additions and 24 deletions
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50
drivers/char/random.c
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@ -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;
@ -860,25 +858,13 @@ 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;
__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 @@ void add_interrupt_randomness(int irq, int irq_flags)
__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);
}