3.16.75-rc1 review patch. If anyone has any objections, please let me know.
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From: Paolo Abeni pabeni@redhat.com
commit 720f1de4021f09898b8c8443f3b3e995991b6e3a upstream.
Currently, the process issuing a "start" command on the pktgen procfs interface, acquires the pktgen thread lock and never release it, until all pktgen threads are completed. The above can blocks indefinitely any other pktgen command and any (even unrelated) netdevice removal - as the pktgen netdev notifier acquires the same lock.
The issue is demonstrated by the following script, reported by Matteo:
ip -b - <<'EOF' link add type dummy link add type veth link set dummy0 up EOF modprobe pktgen echo reset >/proc/net/pktgen/pgctrl { echo rem_device_all echo add_device dummy0 } >/proc/net/pktgen/kpktgend_0 echo count 0 >/proc/net/pktgen/dummy0 echo start >/proc/net/pktgen/pgctrl & sleep 1 rmmod veth
Fix the above releasing the thread lock around the sleep call.
Additionally we must prevent racing with forcefull rmmod - as the thread lock no more protects from them. Instead, acquire a self-reference before waiting for any thread. As a side effect, running
rmmod pktgen
while some thread is running now fails with "module in use" error, before this patch such command hanged indefinitely.
Note: the issue predates the commit reported in the fixes tag, but this fix can't be applied before the mentioned commit.
v1 -> v2: - no need to check for thread existence after flipping the lock, pktgen threads are freed only at net exit time -
Fixes: 6146e6a43b35 ("[PKTGEN]: Removes thread_{un,}lock() macros.") Reported-and-tested-by: Matteo Croce mcroce@redhat.com Signed-off-by: Paolo Abeni pabeni@redhat.com Signed-off-by: David S. Miller davem@davemloft.net Signed-off-by: Ben Hutchings ben@decadent.org.uk --- net/core/pktgen.c | 11 +++++++++++ 1 file changed, 11 insertions(+)
--- a/net/core/pktgen.c +++ b/net/core/pktgen.c @@ -3055,7 +3055,13 @@ static int pktgen_wait_thread_run(struct
if_unlock(t);
+ /* note: 't' will still be around even after the unlock/lock + * cycle because pktgen_thread threads are only cleared at + * net exit + */ + mutex_unlock(&pktgen_thread_lock); msleep_interruptible(100); + mutex_lock(&pktgen_thread_lock);
if (signal_pending(current)) goto signal; @@ -3072,6 +3078,10 @@ static int pktgen_wait_all_threads_run(s struct pktgen_thread *t; int sig = 1;
+ /* prevent from racing with rmmod */ + if (!try_module_get(THIS_MODULE)) + return sig; + mutex_lock(&pktgen_thread_lock);
list_for_each_entry(t, &pn->pktgen_threads, th_list) { @@ -3085,6 +3095,7 @@ static int pktgen_wait_all_threads_run(s t->control |= (T_STOP);
mutex_unlock(&pktgen_thread_lock); + module_put(THIS_MODULE); return sig; }