linux-kernel - [PATCH 2/2] kobject: send KOBJ_REMOVE uevent when the object is removed from sysfs

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Message-Id: <20200524153041.2361-2-gregkh@linuxfoundation.org>
Date:   Sun, 24 May 2020 17:30:41 +0200
From:   Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:     linux-kernel@...r.kernel.org
Cc:     linux@...ck-us.net,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        "Rafael J. Wysocki" <rafael@...nel.org>
Subject: [PATCH 2/2] kobject: send KOBJ_REMOVE uevent when the object is removed from sysfs

It is possible for a KOBJ_REMOVE uevent to be sent to userspace way
after the files are actually gone from sysfs, due to how reference
counting for kobjects work.  This should not be a problem, but it would
be good to properly send the information when things are going away, not
at some later point in time in the future.

Before this move, if a kobject's parent was torn down before the child,
when the call to kobject_uevent() happened, the parent walk to try to
reconstruct the full path of the kobject could be a total mess and cause
crashes.  It's not good to try to tear down a kobject tree from top
down, but let's at least try to not to crash if a user does so.

Cc: "Rafael J. Wysocki" <rafael@...nel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
---
 lib/kobject.c | 14 +++++++-------
 1 file changed, 7 insertions(+), 7 deletions(-)

diff --git a/lib/kobject.c b/lib/kobject.c
index 83198cb37d8d..2509e22ad74a 100644
--- a/lib/kobject.c
+++ b/lib/kobject.c
@@ -620,6 +620,13 @@ void kobject_del(struct kobject *kobj)
 	if (ktype)
 		sysfs_remove_groups(kobj, ktype->default_groups);
 
+	/* send "remove" if the caller did not do it but sent "add" */
+	if (kobj->state_add_uevent_sent && !kobj->state_remove_uevent_sent) {
+		pr_debug("kobject: '%s' (%p): auto cleanup 'remove' event\n",
+			 kobject_name(kobj), kobj);
+		kobject_uevent(kobj, KOBJ_REMOVE);
+	}
+
 	sysfs_remove_dir(kobj);
 	sysfs_put(sd);
 
@@ -673,13 +680,6 @@ static void kobject_cleanup(struct kobject *kobj)
 		pr_debug("kobject: '%s' (%p): does not have a release() function, it is broken and must be fixed. See Documentation/kobject.txt.\n",
 			 kobject_name(kobj), kobj);
 
-	/* send "remove" if the caller did not do it but sent "add" */
-	if (kobj->state_add_uevent_sent && !kobj->state_remove_uevent_sent) {
-		pr_debug("kobject: '%s' (%p): auto cleanup 'remove' event\n",
-			 kobject_name(kobj), kobj);
-		kobject_uevent(kobj, KOBJ_REMOVE);
-	}
-
 	/* remove from sysfs if the caller did not do it */
 	if (kobj->state_in_sysfs) {
 		pr_debug("kobject: '%s' (%p): auto cleanup kobject_del\n",
-- 
2.26.2