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authorBenjamin Herrenschmidt <benh@kernel.crashing.org>2018-07-10 10:29:10 +1000
committerGreg Kroah-Hartman <gregkh@linuxfoundation.org>2019-02-06 17:31:37 +0100
commit2f4da60e2133d85485c9fd4132d34dd6e6b1ebeb (patch)
treef83fd442b47e3ce6f0859ab73f48c5ca33c081ba
parent834adff8b5a711e6e934e75407e88fa4dc123d34 (diff)
drivers: core: Remove glue dirs from sysfs earlier
commit 726e41097920a73e4c7c33385dcc0debb1281e18 upstream. For devices with a class, we create a "glue" directory between the parent device and the new device with the class name. This directory is never "explicitely" removed when empty however, this is left to the implicit sysfs removal done by kobject_release() when the object loses its last reference via kobject_put(). This is problematic because as long as it's not been removed from sysfs, it is still present in the class kset and in sysfs directory structure. The presence in the class kset exposes a use after free bug fixed by the previous patch, but the presence in sysfs means that until the kobject is released, which can take a while (especially with kobject debugging), any attempt at re-creating such as binding a new device for that class/parent pair, will result in a sysfs duplicate file name error. This fixes it by instead doing an explicit kobject_del() when the glue dir is empty, by keeping track of the number of child devices of the gluedir. This is made easy by the fact that all glue dir operations are done with a global mutex, and there's already a function (cleanup_glue_dir) called in all the right places taking that mutex that can be enhanced for this. It appears that this was in fact the intent of the function, but the implementation was wrong. Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org> Acked-by: Linus Torvalds <torvalds@linux-foundation.org> Cc: Guenter Roeck <groeck@google.com> Cc: Zubin Mithra <zsm@chromium.org> Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
-rw-r--r--drivers/base/core.c2
-rw-r--r--include/linux/kobject.h17
2 files changed, 19 insertions, 0 deletions
diff --git a/drivers/base/core.c b/drivers/base/core.c
index 3f463a61f8cf..fc5bbb2519fe 100644
--- a/drivers/base/core.c
+++ b/drivers/base/core.c
@@ -1571,6 +1571,8 @@ static void cleanup_glue_dir(struct device *dev, struct kobject *glue_dir)
return;
mutex_lock(&gdp_mutex);
+ if (!kobject_has_children(glue_dir))
+ kobject_del(glue_dir);
kobject_put(glue_dir);
mutex_unlock(&gdp_mutex);
}
diff --git a/include/linux/kobject.h b/include/linux/kobject.h
index e0a6205caa71..e232df1d9db2 100644
--- a/include/linux/kobject.h
+++ b/include/linux/kobject.h
@@ -117,6 +117,23 @@ extern void kobject_put(struct kobject *kobj);
extern const void *kobject_namespace(struct kobject *kobj);
extern char *kobject_get_path(struct kobject *kobj, gfp_t flag);
+/**
+ * kobject_has_children - Returns whether a kobject has children.
+ * @kobj: the object to test
+ *
+ * This will return whether a kobject has other kobjects as children.
+ *
+ * It does NOT account for the presence of attribute files, only sub
+ * directories. It also assumes there is no concurrent addition or
+ * removal of such children, and thus relies on external locking.
+ */
+static inline bool kobject_has_children(struct kobject *kobj)
+{
+ WARN_ON_ONCE(kref_read(&kobj->kref) == 0);
+
+ return kobj->sd && kobj->sd->dir.subdirs;
+}
+
struct kobj_type {
void (*release)(struct kobject *kobj);
const struct sysfs_ops *sysfs_ops;