From 49b69533e8a62573de987c45cb4469fc8e754723 Mon Sep 17 00:00:00 2001
From: Oleksandr Shchirskyi <oleksandr.shchirskyi@intel.com>
Date: Thu, 14 Jan 2021 15:14:16 +0100
Subject: [PATCH] mdmonitor: check if udev has finished events processing

If mdmonitor is awaken by event, wait for udev to finish
events processing, to eliminate the race between udev and mdadm
when spare has been added and need to be moved by mdmonitor

Signed-off-by: Oleksandr Shchirskyi <oleksandr.shchirskyi@intel.com>
Signed-off-by: Jes Sorensen <jsorensen@fb.com>
---
 Makefile  |  2 +-
 Monitor.c | 75 +++++++++++++++++++++++++++++++++++++++++++++++--------
 2 files changed, 65 insertions(+), 12 deletions(-)

diff --git a/Makefile b/Makefile
index 4cd4c9d8..1e6e1e12 100644
--- a/Makefile
+++ b/Makefile
@@ -119,7 +119,7 @@ endif
 # If you want a static binary, you might uncomment these
 # LDFLAGS = -static
 # STRIP = -s
-LDLIBS=-ldl
+LDLIBS=-ldl -ludev
 
 INSTALL = /usr/bin/install
 DESTDIR =
diff --git a/Monitor.c b/Monitor.c
index 3f3005b8..da1003b4 100644
--- a/Monitor.c
+++ b/Monitor.c
@@ -29,6 +29,7 @@
 #include	<signal.h>
 #include	<limits.h>
 #include	<syslog.h>
+#include	<libudev.h>
 
 struct state {
 	char *devname;
@@ -72,6 +73,7 @@ static int add_new_arrays(struct mdstat_ent *mdstat, struct state **statelist,
 			  int test, struct alert_info *info);
 static void try_spare_migration(struct state *statelist, struct alert_info *info);
 static void link_containers_with_subarrays(struct state *list);
+static int check_udev_activity(void);
 
 int Monitor(struct mddev_dev *devlist,
 	    char *mailaddr, char *alert_cmd,
@@ -129,7 +131,6 @@ int Monitor(struct mddev_dev *devlist,
 	char *mailfrom;
 	struct alert_info info;
 	struct mddev_ident *mdlist;
-	int delay_for_event = c->delay;
 
 	if (!mailaddr) {
 		mailaddr = conf_get_mailaddr();
@@ -244,7 +245,7 @@ int Monitor(struct mddev_dev *devlist,
 
 		/* If an array has active < raid && spare == 0 && spare_group != NULL
 		 * Look for another array with spare > 0 and active == raid and same spare_group
-		 *  if found, choose a device and hotremove/hotadd
+		 * if found, choose a device and hotremove/hotadd
 		 */
 		if (share && anydegraded)
 			try_spare_migration(statelist, &info);
@@ -255,17 +256,12 @@ int Monitor(struct mddev_dev *devlist,
 				break;
 			}
 			else {
-				int wait_result = mdstat_wait(delay_for_event);
-
 				/*
-				 * If mdmonitor is awaken by event, set small delay once
-				 * to deal with udev and mdadm.
+				 * If mdmonitor is awaken by event, check for udev activity
+				 * to wait for udev to finish new devices processing.
 				 */
-				if (wait_result != 0) {
-					if (c->delay > 5)
-						delay_for_event = 5;
-				} else
-					delay_for_event = c->delay;
+				if (mdstat_wait(c->delay) && check_udev_activity())
+					pr_err("Error while waiting for UDEV to complete new devices processing\n");
 
 				mdstat_close();
 			}
@@ -1037,6 +1033,63 @@ static void link_containers_with_subarrays(struct state *list)
 				}
 }
 
+
+/* function: check_udev_activity
+ * Description: Function waits for udev to finish
+ * events processing.
+ * Returns:
+ *		1 - detected error while opening udev
+ *		2 - timeout
+ *		0 - successfull completion
+ */
+static int check_udev_activity(void)
+{
+	struct udev *udev = NULL;
+	struct udev_queue *udev_queue = NULL;
+	int timeout_cnt = 30;
+	int rc = 0;
+
+	/*
+	 * In rare cases systemd may not have udevm,
+	 * in such cases just exit with rc 0
+	 */
+	if (!use_udev())
+		goto out;
+
+	udev = udev_new();
+	if (!udev) {
+		rc = 1;
+		goto out;
+	}
+
+	udev_queue = udev_queue_new(udev);
+	if (!udev_queue) {
+		rc = 1;
+		goto out;
+	}
+
+	if (udev_queue_get_queue_is_empty(udev_queue))
+		goto out;
+
+	while (!udev_queue_get_queue_is_empty(udev_queue)) {
+		sleep(1);
+
+		if (timeout_cnt)
+			timeout_cnt--;
+		else {
+			rc = 2;
+			goto out;
+		}
+	}
+
+out:
+	if (udev_queue)
+		udev_queue_unref(udev_queue);
+	if (udev)
+		udev_unref(udev);
+	return rc;
+}
+
 /* Not really Monitor but ... */
 int Wait(char *dev)
 {
-- 
2.39.2