From: Jason A. Donenfeld Jason@zx2c4.com
commit 534d2eaf1970274150596fdd2bf552721e65d6b2 upstream.
It used to be that mix_interrupt_randomness() would credit 1 bit each time it ran, and so add_interrupt_randomness() would schedule mix() to run every 64 interrupts, a fairly arbitrary number, but nonetheless considered to be a decent enough conservative estimate.
Since e3e33fc2ea7f ("random: do not use input pool from hard IRQs"), mix() is now able to credit multiple bits, depending on the number of calls to add(). This was done for reasons separate from this commit, but it has the nice side effect of enabling this patch to schedule mix() less often.
Currently the rules are: a) Credit 1 bit for every 64 calls to add(). b) Schedule mix() once a second that add() is called. c) Schedule mix() once every 64 calls to add().
Rules (a) and (c) no longer need to be coupled. It's still important to have _some_ value in (c), so that we don't "over-saturate" the fast pool, but the once per second we get from rule (b) is a plenty enough baseline. So, by increasing the 64 in rule (c) to something larger, we avoid calling queue_work_on() as frequently during irq storms.
This commit changes that 64 in rule (c) to be 1024, which means we schedule mix() 16 times less often. And it does *not* need to change the 64 in rule (a).
Fixes: 58340f8e952b ("random: defer fast pool mixing to worker") Cc: stable@vger.kernel.org Cc: Dominik Brodowski linux@dominikbrodowski.net Acked-by: Sebastian Andrzej Siewior bigeasy@linutronix.de Signed-off-by: Jason A. Donenfeld Jason@zx2c4.com Signed-off-by: Greg Kroah-Hartman gregkh@linuxfoundation.org --- drivers/char/random.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-)
--- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -1001,7 +1001,7 @@ void add_interrupt_randomness(int irq) if (new_count & MIX_INFLIGHT) return;
- if (new_count < 64 && !time_is_before_jiffies(fast_pool->last + HZ)) + if (new_count < 1024 && !time_is_before_jiffies(fast_pool->last + HZ)) return;
if (unlikely(!fast_pool->mix.func))