From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932267AbaFKDa2 (ORCPT ); Tue, 10 Jun 2014 23:30:28 -0400 Received: from imap.thunk.org ([74.207.234.97]:60944 "EHLO imap.thunk.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755400AbaFKDaZ (ORCPT ); Tue, 10 Jun 2014 23:30:25 -0400 From: "Theodore Ts'o" To: linux-kernel@vger.kernel.org Cc: "Theodore Ts'o" , George Spelvin Subject: [PATCH 1/3] random: always update the entropy pool under the spinlock Date: Tue, 10 Jun 2014 23:30:18 -0400 Message-Id: <1402457420-2527-2-git-send-email-tytso@mit.edu> X-Mailer: git-send-email 2.0.0 In-Reply-To: <1402457420-2527-1-git-send-email-tytso@mit.edu> References: <1402457420-2527-1-git-send-email-tytso@mit.edu> X-SA-Exim-Connect-IP: X-SA-Exim-Mail-From: tytso@thunk.org X-SA-Exim-Scanned: No (on imap.thunk.org); SAEximRunCond expanded to false Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 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 Cc: George Spelvin --- drivers/char/random.c | 40 +++++++++++++++++++++------------------- 1 file changed, 21 insertions(+), 19 deletions(-) diff --git a/drivers/char/random.c b/drivers/char/random.c index 102c50d..76d2f53 100644 --- a/drivers/char/random.c +++ b/drivers/char/random.c @@ -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++) @@ -860,17 +858,31 @@ 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. + */ + credit = 1; + 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; if (cycles == 0) { if (irq_flags & __IRQF_TIMER) { if (fast_pool->last_timer_intr) @@ -880,16 +892,6 @@ void add_interrupt_randomness(int irq, int irq_flags) 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); } -- 2.0.0