net: sched: refactor tc_ctl_chain() to use block->lock

In order to remove dependency on rtnl lock, modify chain API to use
block->lock to protect chain from concurrent modification. Rearrange
tc_ctl_chain() code to call tcf_chain_hold() while holding block->lock to
prevent concurrent chain removal.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>

diff --git a/net/sched/cls_api.c b/net/sched/cls_api.c
index 2ebf8e53038aab8b9c0fb6ee366f165ecc172109..b5db0f79db14e048ad55d4f3fb1840fd84ce3712 100644 (file)
--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -2255,6 +2255,8 @@ replay:
                err = -EINVAL;
                goto errout_block;
        }
+
+       mutex_lock(&block->lock);
        chain = tcf_chain_lookup(block, chain_index);
        if (n->nlmsg_type == RTM_NEWCHAIN) {
                if (chain) {
@@ -2266,41 +2268,49 @@ replay:
                        } else {
                                NL_SET_ERR_MSG(extack, "Filter chain already exists");
                                err = -EEXIST;
-                               goto errout_block;
+                               goto errout_block_locked;
                        }
                } else {
                        if (!(n->nlmsg_flags & NLM_F_CREATE)) {
                                NL_SET_ERR_MSG(extack, "Need both RTM_NEWCHAIN and NLM_F_CREATE to create a new chain");
                                err = -ENOENT;
-                               goto errout_block;
+                               goto errout_block_locked;
                        }
                        chain = tcf_chain_create(block, chain_index);
                        if (!chain) {
                                NL_SET_ERR_MSG(extack, "Failed to create filter chain");
                                err = -ENOMEM;
-                               goto errout_block;
+                               goto errout_block_locked;
                        }
                }
        } else {
                if (!chain || tcf_chain_held_by_acts_only(chain)) {
                        NL_SET_ERR_MSG(extack, "Cannot find specified filter chain");
                        err = -EINVAL;
-                       goto errout_block;
+                       goto errout_block_locked;
                }
                tcf_chain_hold(chain);
        }
 
+       if (n->nlmsg_type == RTM_NEWCHAIN) {
+               /* Modifying chain requires holding parent block lock. In case
+                * the chain was successfully added, take a reference to the
+                * chain. This ensures that an empty chain does not disappear at
+                * the end of this function.
+                */
+               tcf_chain_hold(chain);
+               chain->explicitly_created = true;
+       }
+       mutex_unlock(&block->lock);
+
        switch (n->nlmsg_type) {
        case RTM_NEWCHAIN:
                err = tc_chain_tmplt_add(chain, net, tca, extack);
-               if (err)
+               if (err) {
+                       tcf_chain_put_explicitly_created(chain);
                        goto errout;
-               /* In case the chain was successfully added, take a reference
-                * to the chain. This ensures that an empty chain
-                * does not disappear at the end of this function.
-                */
-               tcf_chain_hold(chain);
-               chain->explicitly_created = true;
+               }
+
                tc_chain_notify(chain, NULL, 0, NLM_F_CREATE | NLM_F_EXCL,
                                RTM_NEWCHAIN, false);
                break;
@@ -2334,6 +2344,10 @@ errout_block:
                /* Replay the request. */
                goto replay;
        return err;
+
+errout_block_locked:
+       mutex_unlock(&block->lock);
+       goto errout_block;
 }
 
 /* called with RTNL */