From: Manfred Spraul <manf...@colorfullife.com>
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().
Fixes: b16c29191dc8
Signed-off-by: Manfred Spraul <manf...@colorfullife.com>
Cc: <sta...@vger.kernel.org>
Cc: Sasha Levin <sasha.le...@oracle.com>
Cc: Pablo Neira Ayuso <pa...@netfilter.org>
Cc: netfilter-de...@vger.kernel.org
Signed-off-by: Paul E. McKenney <paul...@linux.vnet.ibm.com>
---
net/netfilter/nf_conntrack_core.c | 44 +++++++++++++++++++++------------------
1 file changed, 24 insertions(+), 20 deletions(-)
diff --git a/net/netfilter/nf_conntrack_core.c
b/net/netfilter/nf_conntrack_core.c
index e847dbaa0c6b..1193565c38ae 100644
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -96,19 +96,24 @@ 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 */
+ 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);
@@ -149,18 +154,17 @@ 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]);
}
}
--
2.5.2
