From mboxrd@z Thu Jan 1 00:00:00 1970 From: "Paul E. McKenney" Subject: [PATCH v2 1/9] net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() Date: Wed, 5 Jul 2017 16:31:35 -0700 Message-ID: <1499297503-23852-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <20170705232955.GA15992@linux.vnet.ibm.com> Cc: netfilter-devel@vger.kernel.org, netdev@vger.kernel.org, oleg@redhat.com, akpm@linux-foundation.org, mingo@redhat.com, dave@stgolabs.net, manfred@colorfullife.com, tj@kernel.org, arnd@arndb.de, linux-arch@vger.kernel.org, will.deacon@arm.com, peterz@infradead.org, stern@rowland.harvard.edu, parri.andrea@gmail.com, torvalds@linux-foundation.org, , Sasha Levin , Pablo Neira Ayuso , "Paul E. McKenney" To: linux-kernel@vger.kernel.org Return-path: In-Reply-To: <20170705232955.GA15992@linux.vnet.ibm.com> Sender: stable-owner@vger.kernel.org List-Id: netfilter-devel.vger.kernel.org From: Manfred Spraul As we want to remove spin_unlock_wait() and replace it with explicit spin_lock()/spin_unlock() calls, we can use this to simplify the locking. In addition: - Reading nf_conntrack_locks_all needs ACQUIRE memory ordering. - The new code avoids the backwards loop. Only slightly tested, I did not manage to trigger calls to nf_conntrack_all_lock(). Fixes: b16c29191dc8 Signed-off-by: Manfred Spraul Cc: Cc: Sasha Levin Cc: Pablo Neira Ayuso Cc: netfilter-devel@vger.kernel.org Signed-off-by: Paul E. McKenney --- net/netfilter/nf_conntrack_core.c | 44 +++++++++++++++++++++------------------ 1 file changed, 24 insertions(+), 20 deletions(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index e847dbaa0c6b..1193565c38ae 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -96,19 +96,24 @@ static struct conntrack_gc_work conntrack_gc_work; 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) 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); @@ -149,18 +154,17 @@ 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 - * 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) */ + nf_conntrack_locks_all = true; for (i = 0; i < CONNTRACK_LOCKS; i++) { - spin_unlock_wait(&nf_conntrack_locks[i]); + spin_lock(&nf_conntrack_locks[i]); + + /* This spin_unlock provides the "release" to ensure that + * nf_conntrack_locks_all==true is visible to everyone that + * acquired spin_lock(&nf_conntrack_locks[]). + */ + spin_unlock(&nf_conntrack_locks[i]); } } -- 2.5.2