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) <peterz@infradead.org>
[ Updated the comments. ]
Cc: Andrew Morton <akpm@linux-foundation.org>
Cc: David S. Miller <davem@davemloft.net>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

1 files changed, 22 insertions, 1 deletions

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);
 }