[PATCH v2] ntb: Add mutex to make link_event_callback executed linearly.

[fuyuanli <fuyuanli0722@gmail.com>]

Since the CPU selected by schedule_work is uncertain, multiple link_event
callbacks may be executed at same time. For example, after peer's link is
up, it is down quickly before local link_work completed. If link_cleanup
is added to the workqueue of another CPU, then link_work and link_cleanup
may be executed at the same time. So add a mutex to prevent them from being
executed concurrently.

Signed-off-by: fuyuanli <fuyuanli@didiglobal.com>
---
v2:
1) use guard() instead of lock & unlock functions.

v1:
Link: https://lore.kernel.org/all/aKiBi4ZDlbgzed%2Fz@didi-ThinkCentre-M930t-N000/
---
 drivers/ntb/ntb_transport.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/drivers/ntb/ntb_transport.c b/drivers/ntb/ntb_transport.c
index 4f775c3e218f..eb875e3db2e3 100644
--- a/drivers/ntb/ntb_transport.c
+++ b/drivers/ntb/ntb_transport.c
@@ -59,6 +59,7 @@
 #include <linux/slab.h>
 #include <linux/types.h>
 #include <linux/uaccess.h>
+#include <linux/mutex.h>
 #include "linux/ntb.h"
 #include "linux/ntb_transport.h"
 
@@ -241,6 +242,9 @@ struct ntb_transport_ctx {
 	struct work_struct link_cleanup;
 
 	struct dentry *debugfs_node_dir;
+
+	/* Make sure workq of link event be executed serially */
+	struct mutex link_event_lock;
 };
 
 enum {
@@ -1024,6 +1028,7 @@ static void ntb_transport_link_cleanup_work(struct work_struct *work)
 	struct ntb_transport_ctx *nt =
 		container_of(work, struct ntb_transport_ctx, link_cleanup);
 
+	guard(mutex)(&nt->link_event_lock);
 	ntb_transport_link_cleanup(nt);
 }
 
@@ -1047,6 +1052,8 @@ static void ntb_transport_link_work(struct work_struct *work)
 	u32 val;
 	int rc = 0, i, spad;
 
+	guard(mutex)(&nt->link_event_lock);
+
 	/* send the local info, in the opposite order of the way we read it */
 
 	if (nt->use_msi) {
-- 
2.34.1