[PATCH 3.18 041/145] [PATCH 087/760] net: pktgen: remove rcu locking in pktgen_change_name()

Greg Kroah-Hartman
2017-04-16T10:55:02Z

From: Eric Dumazet <edumazet@google.com>

[ Upstream commit 9a0b1e8ba4061778897b544afc898de2163382f7 ]

After Jesper commit back in linux-3.18, we trigger a lockdep
splat in proc_create_data() while allocating memory from
pktgen_change_name().

This patch converts t->if_lock to a mutex, since it is now only
used from control path, and adds proper locking to pktgen_change_name()

1) pktgen_thread_lock to protect the outer loop (iterating threads)
2) t->if_lock to protect the inner loop (iterating devices)

Note that before Jesper patch, pktgen_change_name() was lacking proper
protection, but lockdep was not able to detect the problem.

Fixes: 8788370a1d4b ("pktgen: RCU-ify "if_list" to remove lock in next_to_run()")
Reported-by: John Sperbeck <jsperbeck@google.com>
Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jesper Dangaard Brouer <brouer@redhat.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
---
net/core/pktgen.c | 17 ++++++++++-------
1 file changed, 10 insertions(+), 7 deletions(-)

--- a/net/core/pktgen.c
+++ b/net/core/pktgen.c
@@ -211,8 +211,8 @@
#define T_REMDEV (1<<3) /* Remove one dev */

/* If lock -- protects updating of if_list */
-#define if_lock(t) spin_lock(&(t->if_lock));
-#define if_unlock(t) spin_unlock(&(t->if_lock));
+#define if_lock(t) mutex_lock(&(t->if_lock));
+#define if_unlock(t) mutex_unlock(&(t->if_lock));

/* Used to help with determining the pkts on receive */
#define PKTGEN_MAGIC 0xbe9be955
@@ -418,7 +418,7 @@ struct pktgen_net {
};

struct pktgen_thread {
- spinlock_t if_lock; /* for list of devices */
+ struct mutex if_lock; /* for list of devices */
struct list_head if_list; /* All device here */
struct list_head th_list;
struct task_struct *tsk;
@@ -1952,11 +1952,13 @@ static void pktgen_change_name(const str
{
struct pktgen_thread *t;

+ mutex_lock(&pktgen_thread_lock);
+
list_for_each_entry(t, &pn->pktgen_threads, th_list) {
struct pktgen_dev *pkt_dev;

- rcu_read_lock();
- list_for_each_entry_rcu(pkt_dev, &t->if_list, list) {
+ if_lock(t);
+ list_for_each_entry(pkt_dev, &t->if_list, list) {
if (pkt_dev->odev != dev)
continue;

@@ -1971,8 +1973,9 @@ static void pktgen_change_name(const str
dev->name);
break;
}
- rcu_read_unlock();
+ if_unlock(t);
}
+ mutex_unlock(&pktgen_thread_lock);
}

static int pktgen_device_event(struct notifier_block *unused,
@@ -3656,7 +3659,7 @@ static int __net_init pktgen_create_thre
return -ENOMEM;
}

- spin_lock_init(&t->if_lock);
+ mutex_init(&t->if_lock);
t->cpu = cpu;

INIT_LIST_HEAD(&t->if_list);