Change the locking for nf_conntrack_lock and nf_conntract_lock_all() to the approach used by ipc/sem.c:
- use smp_store_mb() instead of a raw smp_mb() - use smp_mb__after_spin_lock(). - for nf_conntrack_lock, use spin_lock(&global_lock) instead of spin_unlock_wait(&global_lock) and loop backward. The last change avoids that nf_conntrack_lock() could loop multiple times. Signed-off-by: Manfred Spraul <manf...@colorfullife.com> --- 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 dd2c43a..ded1adc 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -80,20 +80,29 @@ static __read_mostly bool nf_conntrack_locks_all; void nf_conntrack_lock(spinlock_t *lock) __acquires(lock) { + /* Step 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); - } + /* Step 2: make it visible to all CPUs that we hold the lock */ + smp_mb__after_spin_lock(); + + /* Step 3: read locks_all, with ACQUIRE semantics */ + if (likely(smp_load_acquire(&nf_conntrack_locks_all) == false)) + return; + + /* slow path: unlock */ + spin_unlock(lock); + + /* Slow path, step 1: get global lock */ + spin_lock(&nf_conntrack_locks_all_lock); + + /* Slow path, step 2: get the lock we want */ + spin_lock(lock); + + /* Slow path, step 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) @@ -133,15 +142,14 @@ 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]); -- 2.5.5