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@xxxxxxxxxxxxx>
---
net/netfilter/nf_conntrack_core.c | 30 +++++++++++++++++++++++++++++-
1 file changed, 29 insertions(+), 1 deletion(-)
--- a/net/netfilter/nf_conntrack_core.c
+++ b/net/netfilter/nf_conntrack_core.c
@@ -74,7 +74,18 @@ void nf_conntrack_lock(spinlock_t *lock)
spin_lock(lock);
while (unlikely(nf_conntrack_locks_all)) {
spin_unlock(lock);
+ /*
+ * Order the nf_contrack_locks_all load vs the spin_unlock_wait()
+ * loads below, to ensure locks_all is indeed held.
+ */
+ smp_rmb(); /* spin_lock(locks_all) */
spin_unlock_wait(&nf_conntrack_locks_all_lock);
+ /*
+ * The control dependency's LOAD->STORE order is enough to
+ * guarantee the spin_lock() is ordered after the above
+ * unlock_wait(). And the ACQUIRE of the lock ensures we are
+ * fully ordered against the spin_unlock() of locks_all.
+ */
spin_lock(lock);
}
}
@@ -119,14 +130,31 @@ static void nf_conntrack_all_lock(void)
spin_lock(&nf_conntrack_locks_all_lock);
nf_conntrack_locks_all = true;
+ /*
+ * Order the above store against the spin_unlock_wait() loads
+ * below, such that if nf_conntrack_lock() observes lock_all
+ * we must observe lock[] held.
+ */
+ smp_mb(); /* spin_lock(locks_all) */
+
for (i = 0; i < CONNTRACK_LOCKS; i++) {
spin_unlock_wait(&nf_conntrack_locks[i]);
}
+ /*
+ * Ensure we observe all state prior to the spin_unlock()s
+ * observed above.
+ */
+ smp_acquire__after_ctrl_dep();
}
static void nf_conntrack_all_unlock(void)
{
- nf_conntrack_locks_all = false;
+ /*
+ * All prior stores must be complete before we clear locks_all.
+ * Otherwise nf_conntrack_lock() might observe the false but not
+ * the entire critical section.
+ */
+ smp_store_release(&nf_conntrack_locks_all, false);
spin_unlock(&nf_conntrack_locks_all_lock);
}
--
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