From: Vlad Buslov <vladbu@mellanox.com>
Date: Mon, 26 Aug 2019 16:45:02 +0300
Subject: net: sched: conditionally obtain rtnl lock in cls hw offloads API
Patch-mainline: v5.4-rc1
Git-commit: 11bd634da25735a3f2f12112d02661d462a76792
References: bsc#1154353

In order to remove dependency on rtnl lock from offloads code of
classifiers, take rtnl lock conditionally before executing driver
callbacks. Only obtain rtnl lock if block is bound to devices that require
it.

Block bind/unbind code is rtnl-locked and obtains block->cb_lock while
holding rtnl lock. Obtain locks in same order in tc_setup_cb_*() functions
to prevent deadlock.

Signed-off-by: Vlad Buslov <vladbu@mellanox.com>
Acked-by: Jiri Pirko <jiri@mellanox.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Acked-by: Thomas Bogendoerfer <tbogendoerfer@suse.de>
---
 net/sched/cls_api.c |   65 ++++++++++++++++++++++++++++++++++++++++++++++++++++
 1 file changed, 65 insertions(+)

--- a/net/sched/cls_api.c
+++ b/net/sched/cls_api.c
@@ -3076,11 +3076,28 @@ __tc_setup_cb_call(struct tcf_block *blo
 int tc_setup_cb_call(struct tcf_block *block, enum tc_setup_type type,
 		     void *type_data, bool err_stop, bool rtnl_held)
 {
+	bool take_rtnl = READ_ONCE(block->lockeddevcnt) && !rtnl_held;
 	int ok_count;
 
+retry:
+	if (take_rtnl)
+		rtnl_lock();
 	down_read(&block->cb_lock);
+	/* Need to obtain rtnl lock if block is bound to devs that require it.
+	 * In block bind code cb_lock is obtained while holding rtnl, so we must
+	 * obtain the locks in same order here.
+	 */
+	if (!rtnl_held && !take_rtnl && block->lockeddevcnt) {
+		up_read(&block->cb_lock);
+		take_rtnl = true;
+		goto retry;
+	}
+
 	ok_count = __tc_setup_cb_call(block, type, type_data, err_stop);
+
 	up_read(&block->cb_lock);
+	if (take_rtnl)
+		rtnl_unlock();
 	return ok_count;
 }
 EXPORT_SYMBOL(tc_setup_cb_call);
@@ -3095,9 +3112,23 @@ int tc_setup_cb_add(struct tcf_block *bl
 		    enum tc_setup_type type, void *type_data, bool err_stop,
 		    u32 *flags, unsigned int *in_hw_count, bool rtnl_held)
 {
+	bool take_rtnl = READ_ONCE(block->lockeddevcnt) && !rtnl_held;
 	int ok_count;
 
+retry:
+	if (take_rtnl)
+		rtnl_lock();
 	down_read(&block->cb_lock);
+	/* Need to obtain rtnl lock if block is bound to devs that require it.
+	 * In block bind code cb_lock is obtained while holding rtnl, so we must
+	 * obtain the locks in same order here.
+	 */
+	if (!rtnl_held && !take_rtnl && block->lockeddevcnt) {
+		up_read(&block->cb_lock);
+		take_rtnl = true;
+		goto retry;
+	}
+
 	/* Make sure all netdevs sharing this block are offload-capable. */
 	if (block->nooffloaddevcnt && err_stop) {
 		ok_count = -EOPNOTSUPP;
@@ -3115,6 +3146,8 @@ int tc_setup_cb_add(struct tcf_block *bl
 					  ok_count, true);
 err_unlock:
 	up_read(&block->cb_lock);
+	if (take_rtnl)
+		rtnl_unlock();
 	return ok_count < 0 ? ok_count : 0;
 }
 EXPORT_SYMBOL(tc_setup_cb_add);
@@ -3131,9 +3164,23 @@ int tc_setup_cb_replace(struct tcf_block
 			u32 *new_flags, unsigned int *new_in_hw_count,
 			bool rtnl_held)
 {
+	bool take_rtnl = READ_ONCE(block->lockeddevcnt) && !rtnl_held;
 	int ok_count;
 
+retry:
+	if (take_rtnl)
+		rtnl_lock();
 	down_read(&block->cb_lock);
+	/* Need to obtain rtnl lock if block is bound to devs that require it.
+	 * In block bind code cb_lock is obtained while holding rtnl, so we must
+	 * obtain the locks in same order here.
+	 */
+	if (!rtnl_held && !take_rtnl && block->lockeddevcnt) {
+		up_read(&block->cb_lock);
+		take_rtnl = true;
+		goto retry;
+	}
+
 	/* Make sure all netdevs sharing this block are offload-capable. */
 	if (block->nooffloaddevcnt && err_stop) {
 		ok_count = -EOPNOTSUPP;
@@ -3155,6 +3202,8 @@ int tc_setup_cb_replace(struct tcf_block
 					  new_flags, ok_count, true);
 err_unlock:
 	up_read(&block->cb_lock);
+	if (take_rtnl)
+		rtnl_unlock();
 	return ok_count < 0 ? ok_count : 0;
 }
 EXPORT_SYMBOL(tc_setup_cb_replace);
@@ -3167,9 +3216,23 @@ int tc_setup_cb_destroy(struct tcf_block
 			enum tc_setup_type type, void *type_data, bool err_stop,
 			u32 *flags, unsigned int *in_hw_count, bool rtnl_held)
 {
+	bool take_rtnl = READ_ONCE(block->lockeddevcnt) && !rtnl_held;
 	int ok_count;
 
+retry:
+	if (take_rtnl)
+		rtnl_lock();
 	down_read(&block->cb_lock);
+	/* Need to obtain rtnl lock if block is bound to devs that require it.
+	 * In block bind code cb_lock is obtained while holding rtnl, so we must
+	 * obtain the locks in same order here.
+	 */
+	if (!rtnl_held && !take_rtnl && block->lockeddevcnt) {
+		up_read(&block->cb_lock);
+		take_rtnl = true;
+		goto retry;
+	}
+
 	ok_count = __tc_setup_cb_call(block, type, type_data, err_stop);
 
 	tc_cls_offload_cnt_reset(block, tp, in_hw_count, flags);
@@ -3177,6 +3240,8 @@ int tc_setup_cb_destroy(struct tcf_block
 		tp->ops->hw_del(tp, type_data);
 
 	up_read(&block->cb_lock);
+	if (take_rtnl)
+		rtnl_unlock();
 	return ok_count < 0 ? ok_count : 0;
 }
 EXPORT_SYMBOL(tc_setup_cb_destroy);