From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S934769AbcHaNm4 (ORCPT ); Wed, 31 Aug 2016 09:42:56 -0400 Received: from mail-wm0-f65.google.com ([74.125.82.65]:34113 "EHLO mail-wm0-f65.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S934598AbcHaNmw (ORCPT ); Wed, 31 Aug 2016 09:42:52 -0400 From: Manfred Spraul To: benh@kernel.crashing.org, paulmck@linux.vnet.ibm.com, Ingo Molnar , Boqun Feng , Peter Zijlstra , Andrew Morton Cc: LKML , 1vier1@web.de, Davidlohr Bueso , Manfred Spraul , Pablo Neira Ayuso , netfilter-devel@vger.kernel.org Subject: [PATCH 5/5] net/netfilter/nf_conntrack_core: update memory barriers. Date: Wed, 31 Aug 2016 15:42:30 +0200 Message-Id: <1472650950-3131-6-git-send-email-manfred@colorfullife.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1472650950-3131-1-git-send-email-manfred@colorfullife.com> References: <1472650950-3131-1-git-send-email-manfred@colorfullife.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org As explained in commit 51d7d5205d33 ("powerpc: Add smp_mb() to arch_spin_is_locked()", for some architectures the ACQUIRE during spin_lock only applies to loading the lock, not to storing the lock state. nf_conntrack_lock() does not handle this correctly: /* 1) Acquire the lock */ spin_lock(lock); while (unlikely(nf_conntrack_locks_all)) { spin_unlock(lock); spinlock_store_acquire() is missing between spin_lock and reading nf_conntrack_locks_all. In addition, reading nf_conntrack_locks_all needs ACQUIRE memory ordering. 2nd, minor issue: If there would be many nf_conntrack_all_lock() callers, then nf_conntrack_lock() would loop forever. Therefore: Change nf_conntrack_lock and nf_conntract_lock_all() to the approach used by ipc/sem.c: - add spinlock_store_acquire() - add smp_load_acquire() - for nf_conntrack_lock, use spin_lock(&global_lock) instead of spin_unlock_wait(&global_lock) and loop backward. - use smp_store_mb() instead of a raw smp_mb() Signed-off-by: Manfred Spraul Cc: Pablo Neira Ayuso Cc: netfilter-devel@vger.kernel.org --- Question: Should I split this patch? First a patch that uses smp_mb(), with Cc: stable. The replace the smp_mb() with spinlock_store_acquire, not for stable net/netfilter/nf_conntrack_core.c | 36 ++++++++++++++++++++++-------------- 1 file changed, 22 insertions(+), 14 deletions(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 7d90a5d..f840b0b 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -79,20 +79,29 @@ static __read_mostly bool nf_conntrack_locks_all; void nf_conntrack_lock(spinlock_t *lock) __acquires(lock) { + /* 1) Acquire the lock */ spin_lock(lock); - while (unlikely(nf_conntrack_locks_all)) { - spin_unlock(lock); - /* - * Order the 'nf_conntrack_locks_all' load vs. the - * spin_unlock_wait() loads below, to ensure - * that 'nf_conntrack_locks_all_lock' is indeed held: - */ - smp_rmb(); /* spin_lock(&nf_conntrack_locks_all_lock) */ - spin_unlock_wait(&nf_conntrack_locks_all_lock); - spin_lock(lock); - } + /* 2) Order storing the lock and reading nf_conntrack_locks_all */ + spinlock_store_acquire(); + + /* 3) read nf_conntrack_locks_all, with ACQUIRE semantics */ + if (likely(smp_load_acquire(&nf_conntrack_locks_all) == false)) + return; + + /* fast path failed, unlock */ + spin_unlock(lock); + + /* Slow path 1) get global lock */ + spin_lock(&nf_conntrack_locks_all_lock); + + /* Slow path 2) get the lock we want */ + spin_lock(lock); + + /* Slow path 3) release the global lock */ + spin_unlock(&nf_conntrack_locks_all_lock); } + EXPORT_SYMBOL_GPL(nf_conntrack_lock); static void nf_conntrack_double_unlock(unsigned int h1, unsigned int h2) @@ -132,15 +141,14 @@ static void nf_conntrack_all_lock(void) int i; spin_lock(&nf_conntrack_locks_all_lock); - nf_conntrack_locks_all = true; /* - * Order the above store of 'nf_conntrack_locks_all' against + * Order the store of 'nf_conntrack_locks_all' against * the spin_unlock_wait() loads below, such that if * nf_conntrack_lock() observes 'nf_conntrack_locks_all' * we must observe nf_conntrack_locks[] held: */ - smp_mb(); /* spin_lock(&nf_conntrack_locks_all_lock) */ + smp_store_mb(nf_conntrack_locks_all, true); for (i = 0; i < CONNTRACK_LOCKS; i++) { spin_unlock_wait(&nf_conntrack_locks[i]); -- 2.7.4