Commit-ID: 3ef0c7a730de0bae03d86c19570af764fa3c4445 Gitweb: http://git.kernel.org/tip/3ef0c7a730de0bae03d86c19570af764fa3c4445 Author: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> AuthorDate: Thu, 6 Jul 2017 20:45:59 +0200 Committer: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> CommitDate: Tue, 25 Jul 2017 10:08:58 -0700 net/netfilter/nf_conntrack_core: Fix net_conntrack_lock() 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(). V2: With improved comments, to clearly show how the barriers pair. Fixes: b16c29191dc8 ("netfilter: nf_conntrack: use safer way to lock all buckets") Signed-off-by: Manfred Spraul <manfred@xxxxxxxxxxxxxxxx> Cc: <stable@xxxxxxxxxxxxxxx> Cc: Alan Stern <stern@xxxxxxxxxxxxxxxxxxx> Cc: Sasha Levin <sasha.levin@xxxxxxxxxx> Cc: Pablo Neira Ayuso <pablo@xxxxxxxxxxxxx> Cc: netfilter-devel@xxxxxxxxxxxxxxx Signed-off-by: Paul E. McKenney <paulmck@xxxxxxxxxxxxxxxxxx> --- net/netfilter/nf_conntrack_core.c | 52 ++++++++++++++++++++++----------------- 1 file changed, 29 insertions(+), 23 deletions(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index 9979f46..51390fe 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -96,19 +96,26 @@ 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 + * It pairs with the smp_store_release() in nf_conntrack_all_unlock() + */ + 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); @@ -149,28 +156,27 @@ 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]); } } static void nf_conntrack_all_unlock(void) { - /* - * All prior stores must be complete before we clear + /* All prior stores must be complete before we clear * 'nf_conntrack_locks_all'. Otherwise nf_conntrack_lock() * might observe the false value but not the entire - * critical section: + * critical section. + * It pairs with the smp_load_acquire() in nf_conntrack_lock() */ smp_store_release(&nf_conntrack_locks_all, false); spin_unlock(&nf_conntrack_locks_all_lock);