On 11/26/2020 2:46 PM, Elad Nachman wrote:
This patch leverages on Stephen Hemminger's 64106 patch from Dec 2019,
and fixes the issues reported by Ferruh and Igor:
A. KNI sync lock is being locked while rtnl is held.
If two threads are calling kni_net_process_request() ,
then the first one wil take the sync lock, release rtnl lock then sleep.
The second thread will try to lock sync lock while holding rtnl.
The first thread will wake, and try to lock rtnl, resulting in a deadlock.
The remedy is to release rtnl before locking the KNI sync lock.
Since in between nothing is accessing Linux network-wise,
no rtnl locking is needed.
Hi Elad,
Thanks for explanation, that clarifies the issue.
Also I confirm I don't see the hang, at least as much as I test.
B. There is a race condition in __dev_close_many() processing the
close_list while the application terminates.
It looks like if two vEth devices are terminating,
and one releases the rtnl lock, the other takes it,
updating the close_list in an unstable state,
causing the close_list to become a circular linked list,
hence list_for_each_entry() will endlessly loop inside
__dev_close_many() .
Since the description for the original patch indicate the
original motivation was bringing the device up,
I have changed kni_net_process_request() to hold the rtnl mutex
in case of bringing the device down since this is the path called
from __dev_close_many() , causing the corruption of the close_list.
I can't reproduce this case, I see the protection in the code, but better to get
confirmation from Igor.
Overall the issue seems calling a function pointed by 'rte_kni_ops' which
requires to acquire the rtnl lock.
So I wonder if this can't be handled in the ops function, by processing the
request asynchronously,
like recording the request, return from 'rte_kni_ops', and process the request
afterwards?
I assume the application we mention is not kni sample application.
Signed-off-by: Elad Nachman <ela...@gmail.com>
---
kernel/linux/kni/kni_net.c | 47 +++++++++++++++++++++++++-------------
1 file changed, 31 insertions(+), 16 deletions(-)
diff --git a/kernel/linux/kni/kni_net.c b/kernel/linux/kni/kni_net.c
index 4b752083d..cf5b0845d 100644
--- a/kernel/linux/kni/kni_net.c
+++ b/kernel/linux/kni/kni_net.c
@@ -17,6 +17,7 @@
#include <linux/skbuff.h>
#include <linux/kthread.h>
#include <linux/delay.h>
+#include <linux/rtnetlink.h>
#include <rte_kni_common.h>
#include <kni_fifo.h>
@@ -102,18 +103,26 @@ get_data_kva(struct kni_dev *kni, void *pkt_kva)
* It can be called to process the request.
*/
static int
-kni_net_process_request(struct kni_dev *kni, struct rte_kni_request *req)
+kni_net_process_request(struct net_device *dev, struct rte_kni_request *req)
{
+ struct kni_dev *kni = netdev_priv(dev);
int ret = -1;
void *resp_va;
uint32_t num;
int ret_val;
+ int req_is_dev_stop = 0;
- if (!kni || !req) {
- pr_err("No kni instance or request\n");
- return -EINVAL;
- }
+ if (req->req_id == RTE_KNI_REQ_CFG_NETWORK_IF &&
+ req->if_up == 0)
+ req_is_dev_stop = 1;
+ ASSERT_RTNL();
+
+ if (!req_is_dev_stop) {
+ dev_hold(dev);
+ rtnl_unlock();
+ }
+
mutex_lock(&kni->sync_lock);
/* Construct data */
@@ -125,8 +134,13 @@ kni_net_process_request(struct kni_dev *kni, struct
rte_kni_request *req)
goto fail;
}
+ /* Since we need to wait and RTNL mutex is held
+ * drop the mutex and hold refernce to keep device
+ */
+
Comment seems left here, need to go up. s/refernce/reference
ret_val = wait_event_interruptible_timeout(kni->wq,
kni_fifo_count(kni->resp_q), 3 * HZ);
+
if (signal_pending(current) || ret_val <= 0) {
ret = -ETIME;
goto fail;
@@ -144,6 +158,13 @@ kni_net_process_request(struct kni_dev *kni, struct
rte_kni_request *req)
fail:
mutex_unlock(&kni->sync_lock);
+
+
extra empty line
+ if (!req_is_dev_stop) {
+ rtnl_lock();
+ dev_put(dev);
+ }
+
return ret;
}
@@ -155,7 +176,6 @@ kni_net_open(struct net_device *dev)
{
int ret;
struct rte_kni_request req;
- struct kni_dev *kni = netdev_priv(dev);
netif_start_queue(dev);
if (kni_dflt_carrier == 1)
@@ -168,7 +188,7 @@ kni_net_open(struct net_device *dev)
/* Setting if_up to non-zero means up */
req.if_up = 1;
- ret = kni_net_process_request(kni, &req);
+ ret = kni_net_process_request(dev, &req);
Althoug it is not soo confusing, these lines and following ones are noise for
this patch, they are just for 'kni_net_process_request' paramter change.
What do you think do the 'kni_net_process_request' parameter change in first
patch, and fix the issue in second, this way second patch can contain only the
actual changes required for fix.
