From: Sahithi Singam
<sahithi.sin...@oracle.com<mailto:sahithi.sin...@oracle.com>>
Async user request changes resulted in a kernel deadlock when used with linux
kernel version>= 5.12.
Starting from linux kernel version 5.12, a new global semaphore dev_addr_sem
was introduced in dev_set_mac_address_user() function that should be acquired
and released along with rtnl_lock when a mac address set request was received
from userspace.
When a mac address set request is received on KNI interface, before sending
request to userspace, kni code is releasing rtnl_lock without releasing
dev_addr_sem semaphore. After receiving a response it is again trying to hold
rtnl_lock. These changes were added as part of async user request changes to
fix a kernel deadlock with bifurcated devices.
This code is resulting in deadlock as kni is just releasing rtnl_lock without
releasing semaphore while mac address set request on some other device could
have acquired rtnl_lock and could be waiting for dev_addr_sem held by the
current device.
As a solution, support async user request changes based on a module parameter.
This will limit kernel deadlock issue to users using KNI over bifurcated
devices with kernel versions >= 5.12.
Bugzilla ID: 816
Fixes: 631217c76135 ("kni: fix kernel deadlock with bifurcated device")
Cc: ela...@gmail.com<mailto:ela...@gmail.com>
Signed-off-by: Sahithi Singam
<sahithi.sin...@oracle.com<mailto:sahithi.sin...@oracle.com>>
---
kernel/linux/kni/kni_dev.h | 3 +++
kernel/linux/kni/kni_misc.c | 11 +++++++++++ kernel/linux/kni/kni_net.c | 46
++++++++++++++++++++++++++-------------------
3 files changed, 41 insertions(+), 19 deletions(-)
diff --git a/kernel/linux/kni/kni_dev.h b/kernel/linux/kni/kni_dev.h index
c15da311..ea9d23a 100644
--- a/kernel/linux/kni/kni_dev.h
+++ b/kernel/linux/kni/kni_dev.h
@@ -34,6 +34,9 @@
/* Default carrier state for created KNI network interfaces */ extern uint32_t
kni_dflt_carrier;
+/* Asynchronous userspace request support */ extern int async_support;
+
/**
* A structure describing the private information for a kni device.
*/
diff --git a/kernel/linux/kni/kni_misc.c b/kernel/linux/kni/kni_misc.c index
2b464c4..685067d 100644
--- a/kernel/linux/kni/kni_misc.c
+++ b/kernel/linux/kni/kni_misc.c
@@ -41,6 +41,9 @@
static char *carrier;
uint32_t kni_dflt_carrier;
+/* Asynchronous userspace request support */ int async_support;
+
#define KNI_DEV_IN_USE_BIT_NUM 0 /* Bit number for device in use */
static int kni_net_id;
@@ -659,3 +662,11 @@ struct kni_net {
"\t\ton Interfaces will be created with carrier state set to on.\n"
"\t\t"
);
+
+module_param(async_support, int, 0);
+MODULE_PARM_DESC(async_support,
+"Support KNI async user request (default=0):\n"
+"\t\t0 Async user request not supported.\n"
+"\t\tother Async user request supported.\n"
+"\t\t"
+);
diff --git a/kernel/linux/kni/kni_net.c b/kernel/linux/kni/kni_net.c index
611719b..664f4b7 100644
--- a/kernel/linux/kni/kni_net.c
+++ b/kernel/linux/kni/kni_net.c
@@ -111,14 +111,16 @@
uint32_t num;
int ret_val;
- ASSERT_RTNL();
+ if (async_support != 0) {
+ ASSERT_RTNL();
- /* If we need to wait and RTNL mutex is held
- * drop the mutex and hold reference to keep device
- */
- if (req->async == 0) {
- dev_hold(dev);
- rtnl_unlock();
+ /* If we need to wait and RTNL mutex is held
+ * drop the mutex and hold reference to keep device
+ */
+ if (req->async == 0) {
+ dev_hold(dev);
+ rtnl_unlock();
+ }
}
mutex_lock(&kni->sync_lock);
@@ -132,12 +134,15 @@
goto fail;
}
- /* No result available since request is handled
- * asynchronously. set response to success.
- */
- if (req->async != 0) {
- req->result = 0;
- goto async;
+ if (async_support != 0) {
+ /* No result available since request is handled
+ * asynchronously. set response to success.
+ */
+ if (req->async != 0) {
+ req->result = 0;
+ ret = 0;
+ goto fail;
+ }
}
ret_val = wait_event_interruptible_timeout(kni->wq,
@@ -155,14 +160,15 @@
}
memcpy(req, kni->sync_kva, sizeof(struct rte_kni_request));
-async:
ret = 0;
fail:
mutex_unlock(&kni->sync_lock);
- if (req->async == 0) {
- rtnl_lock();
- dev_put(dev);
+ if (async_support != 0) {
+ if (req->async == 0) {
+ rtnl_lock();
+ dev_put(dev);
+ }
}
return ret;
}
@@ -207,8 +213,10 @@
/* Setting if_up to 0 means down */
req.if_up = 0;
- /* request async because of the deadlock problem */
- req.async = 1;
+ if (async_support != 0) {
+ /* request async because of the deadlock problem */
+ req.async = 1;
+ }
ret = kni_net_process_request(dev, &req);
--
1.8.3.1
