Re: net: sleeping function called from invalid context in net_enable_timestamp

[Eric Dumazet]

On Wed, 2017-03-01 at 11:59 -0800, Eric Dumazet wrote:
> On Wed, Mar 1, 2017 at 11:51 AM, Dmitry Vyukov <dvyu...@google.com> wrote:
> >
> > Hello,
> >
> > I've got the following report while running syzkaller fuzzer on
> > e5d56efc97f8240d0b5d66c03949382b6d7e5570
> 
> 
> 
> Right, a listener is playing fool games.
> 
> We need to use a work queue for all net_enable_timestamp() invocations

Something like :

diff --git a/net/core/dev.c b/net/core/dev.c
index 
e63bf61b19be029e30ac40443c0e2edb24de4a73..10fac295f4d4dff983156e2cac22456db948b32b
 100644
--- a/net/core/dev.c
+++ b/net/core/dev.c
@@ -1702,15 +1702,27 @@ static void netstamp_clear(struct work_struct *work)
 {
        int deferred = atomic_xchg(&netstamp_needed_deferred, 0);
 
-       while (deferred--)
+       while (deferred < 0) {
+               deferred++;
                static_key_slow_dec(&netstamp_needed);
+       }
+       while (deferred > 0) {
+               deferred--;
+               static_key_slow_inc(&netstamp_needed);
+       }
 }
 static DECLARE_WORK(netstamp_work, netstamp_clear);
 #endif
 
 void net_enable_timestamp(void)
 {
+#ifdef HAVE_JUMP_LABEL
+       /* net_enable_timestamp() can be called from non process context */
+       atomic_inc(&netstamp_needed_deferred);
+       schedule_work(&netstamp_work);
+#else
        static_key_slow_inc(&netstamp_needed);
+#endif
 }
 EXPORT_SYMBOL(net_enable_timestamp);
 
@@ -1718,7 +1730,7 @@ void net_disable_timestamp(void)
 {
 #ifdef HAVE_JUMP_LABEL
        /* net_disable_timestamp() can be called from non process context */
-       atomic_inc(&netstamp_needed_deferred);
+       atomic_dec(&netstamp_needed_deferred);
        schedule_work(&netstamp_work);
 #else
        static_key_slow_dec(&netstamp_needed);