Messages in this thread Patch in this message | | | From | Manfred Spraul <> | Subject | [PATCH 3/4 V4] net/netfilter/nf_conntrack_core: update memory barriers. | Date | Mon, 29 Aug 2016 15:34:28 +0200 |
| |
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 <manfred@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 7d90a5d..4ed229b 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 writing the lock and reading nf_conntrack_locks_all */ + smp_mb__after_spin_lock(); + + /* 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]); -- 2.5.5
| |