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[dm-devel] [PATCH] Use refcounting for sysfs devices



As we're caching sysfs devices we need to introduce some sort
of refcounting here. Otherwise the device might be removed from
other threads while we're still accessing it.

References: bnc#642846

Signed-off-by: Hannes Reinecke <hare suse de>

diff --git a/libmultipath/sysfs.c b/libmultipath/sysfs.c
index fc64881..ff63a1b 100644
--- a/libmultipath/sysfs.c
+++ b/libmultipath/sysfs.c
@@ -44,6 +44,7 @@ static LIST_HEAD(sysfs_dev_list);
 struct sysfs_dev {
 	struct list_head node;
 	struct sysfs_device dev;
+	int refcount;
 };
 
 int sysfs_init(char *path, size_t len)
@@ -152,6 +153,7 @@ struct sysfs_device *sysfs_device_get(const char *devpath)
 			if (strcmp(sysdev_loop->dev.devpath, devpath_real) == 0) {
 				dbg("found vanished dev in cache '%s'",
 				    sysdev_loop->dev.devpath);
+				sysdev_loop->refcount++;
 				return &sysdev_loop->dev;
 			}
 		}
@@ -167,6 +169,7 @@ struct sysfs_device *sysfs_device_get(const char *devpath)
 		if (strcmp(sysdev_loop->dev.devpath, devpath_real) == 0) {
 			dbg("found dev in cache '%s'", sysdev_loop->dev.devpath);
 			dev = &sysdev_loop->dev;
+			sysdev_loop->refcount++;
 		}
 	}
 
@@ -177,6 +180,7 @@ struct sysfs_device *sysfs_device_get(const char *devpath)
 		if (sysdev == NULL)
 			return NULL;
 		memset(sysdev, 0x00, sizeof(struct sysfs_dev));
+		sysdev->refcount = 1;
 		list_add(&sysdev->node, &sysfs_dev_list);
 		dev = &sysdev->dev;
 	}
@@ -243,6 +247,8 @@ struct sysfs_device *sysfs_device_verify(struct sysfs_device *dev)
 	char path[PATH_SIZE];
 	struct stat statbuf;
 
+	if (!dev->devpath)
+		return NULL;
 	strlcpy(path, sysfs_path, sizeof(path));
 	strlcat(path, dev->devpath, sizeof(path));
 	if (stat(dev->devpath, &statbuf) == 0 &&
@@ -258,15 +264,21 @@ void sysfs_device_put(struct sysfs_device *dev)
 
 	list_for_each_entry(sysdev_loop, &sysfs_dev_list, node) {
 		if (&sysdev_loop->dev == dev) {
-			dbg("removed dev '%s' from cache",
-			    sysdev_loop->dev.devpath);
-			list_del(&sysdev_loop->node);
-			free(sysdev_loop);
+			sysdev_loop->refcount--;
+			if (!sysdev_loop->refcount) {
+				dbg("removed dev '%s' from cache",
+				    sysdev_loop->dev.devpath);
+				list_del(&sysdev_loop->node);
+				free(sysdev_loop);
+			} else {
+				dbg("dev '%s' still in cache, refcount %d",
+				    sysdev_loop->dev.devpath,
+				    sysdev_loop->refcount);
+			}
 			return;
 		}
 	}
-	dbg("dev '%s' not found in cache",
-	    sysdev_loop->dev.devpath);
+	dbg("dev '%s' not found in cache", dev->devpath);
 
 	return;
 }


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