From b316ff783d17bd6217804e2e4385ce9347d7dad9 Mon Sep 17 00:00:00 2001 From: Peter Zijlstra Date: Tue, 24 May 2016 15:00:38 +0200 Subject: [PATCH] locking/spinlock, netfilter: Fix nf_conntrack_lock() barriers Even with spin_unlock_wait() fixed, nf_conntrack_lock{,_all}() is borken as it misses a bunch of memory barriers to order the whole global vs local locks scheme. Even x86 (and other TSO archs) are affected. Signed-off-by: Peter Zijlstra (Intel) [ Updated the comments. ] Cc: Andrew Morton Cc: David S. Miller Cc: Linus Torvalds Cc: Paul E. McKenney Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: linux-kernel@vger.kernel.org Signed-off-by: Ingo Molnar --- net/netfilter/nf_conntrack_core.c | 23 ++++++++++++++++++++++- 1 file changed, 22 insertions(+), 1 deletion(-) diff --git a/net/netfilter/nf_conntrack_core.c b/net/netfilter/nf_conntrack_core.c index db2312eeb2a4..b8c5501d3872 100644 --- a/net/netfilter/nf_conntrack_core.c +++ b/net/netfilter/nf_conntrack_core.c @@ -83,6 +83,13 @@ void nf_conntrack_lock(spinlock_t *lock) __acquires(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); } @@ -128,6 +135,14 @@ static void nf_conntrack_all_lock(void) 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) */ + for (i = 0; i < CONNTRACK_LOCKS; i++) { spin_unlock_wait(&nf_conntrack_locks[i]); } @@ -135,7 +150,13 @@ static void nf_conntrack_all_lock(void) static void nf_conntrack_all_unlock(void) { - nf_conntrack_locks_all = false; + /* + * 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: + */ + smp_store_release(&nf_conntrack_locks_all, false); spin_unlock(&nf_conntrack_locks_all_lock); }