From d3d40f237480abf3268956daf18cdc56edd32834 Mon Sep 17 00:00:00 2001 From: Mark Tomlinson Date: Mon, 8 Mar 2021 14:24:12 +1300 Subject: Revert "netfilter: x_tables: Switch synchronization to RCU" This reverts commit cc00bcaa589914096edef7fb87ca5cee4a166b5c. This (and the preceding) patch basically re-implemented the RCU mechanisms of patch 784544739a25. That patch was replaced because of the performance problems that it created when replacing tables. Now, we have the same issue: the call to synchronize_rcu() makes replacing tables slower by as much as an order of magnitude. Prior to using RCU a script calling "iptables" approx. 200 times was taking 1.16s. With RCU this increased to 11.59s. Revert these patches and fix the issue in a different way. Signed-off-by: Mark Tomlinson Signed-off-by: Pablo Neira Ayuso --- net/netfilter/x_tables.c | 49 +++++++++++++++++++++++++++++++++--------------- 1 file changed, 34 insertions(+), 15 deletions(-) (limited to 'net/netfilter') diff --git a/net/netfilter/x_tables.c b/net/netfilter/x_tables.c index bce6ca203d46..7df3aef39c5c 100644 --- a/net/netfilter/x_tables.c +++ b/net/netfilter/x_tables.c @@ -1351,14 +1351,6 @@ struct xt_counters *xt_counters_alloc(unsigned int counters) } EXPORT_SYMBOL(xt_counters_alloc); -struct xt_table_info -*xt_table_get_private_protected(const struct xt_table *table) -{ - return rcu_dereference_protected(table->private, - mutex_is_locked(&xt[table->af].mutex)); -} -EXPORT_SYMBOL(xt_table_get_private_protected); - struct xt_table_info * xt_replace_table(struct xt_table *table, unsigned int num_counters, @@ -1366,6 +1358,7 @@ xt_replace_table(struct xt_table *table, int *error) { struct xt_table_info *private; + unsigned int cpu; int ret; ret = xt_jumpstack_alloc(newinfo); @@ -1375,20 +1368,47 @@ xt_replace_table(struct xt_table *table, } /* Do the substitution. */ - private = xt_table_get_private_protected(table); + local_bh_disable(); + private = table->private; /* Check inside lock: is the old number correct? */ if (num_counters != private->number) { pr_debug("num_counters != table->private->number (%u/%u)\n", num_counters, private->number); + local_bh_enable(); *error = -EAGAIN; return NULL; } newinfo->initial_entries = private->initial_entries; + /* + * Ensure contents of newinfo are visible before assigning to + * private. + */ + smp_wmb(); + table->private = newinfo; + + /* make sure all cpus see new ->private value */ + smp_wmb(); - rcu_assign_pointer(table->private, newinfo); - synchronize_rcu(); + /* + * Even though table entries have now been swapped, other CPU's + * may still be using the old entries... + */ + local_bh_enable(); + + /* ... so wait for even xt_recseq on all cpus */ + for_each_possible_cpu(cpu) { + seqcount_t *s = &per_cpu(xt_recseq, cpu); + u32 seq = raw_read_seqcount(s); + + if (seq & 1) { + do { + cond_resched(); + cpu_relax(); + } while (seq == raw_read_seqcount(s)); + } + } audit_log_nfcfg(table->name, table->af, private->number, !private->number ? AUDIT_XT_OP_REGISTER : @@ -1424,12 +1444,12 @@ struct xt_table *xt_register_table(struct net *net, } /* Simplifies replace_table code. */ - rcu_assign_pointer(table->private, bootstrap); + table->private = bootstrap; if (!xt_replace_table(table, 0, newinfo, &ret)) goto unlock; - private = xt_table_get_private_protected(table); + private = table->private; pr_debug("table->private->number = %u\n", private->number); /* save number of initial entries */ @@ -1452,8 +1472,7 @@ void *xt_unregister_table(struct xt_table *table) struct xt_table_info *private; mutex_lock(&xt[table->af].mutex); - private = xt_table_get_private_protected(table); - RCU_INIT_POINTER(table->private, NULL); + private = table->private; list_del(&table->list); mutex_unlock(&xt[table->af].mutex); audit_log_nfcfg(table->name, table->af, private->number, -- cgit v1.2.3