From: MengEn Sun <mengensun@tencent.com>
Date: Fri, 6 Dec 2024 04:13:47 +0000 (+0800)
Subject: ucounts: move kfree() out of critical zone protected by ucounts_lock
X-Git-Tag: v6.14-rc1~78^2~117
X-Git-Url: http://git.ipfire.org/?a=commitdiff_plain;h=f49b42d415a32faee6bc08923821f432f64a4e90;p=thirdparty%2Fkernel%2Flinux.git

ucounts: move kfree() out of critical zone protected by ucounts_lock

Although kfree is a non-sleep function, it is possible to enter a long
chain of calls probabilistically, so it looks better to move kfree from
alloc_ucounts() out of the critical zone of ucounts_lock.

Link: https://lkml.kernel.org/r/1733458427-11794-1-git-send-email-mengensun@tencent.com
Signed-off-by: MengEn Sun <mengensun@tencent.com>
Reviewed-by: YueHong Wu <yuehongwu@tencent.com>
Reviewed-by: Andrew Morton <akpm@linux-foundation.org>
Cc: Andrei Vagin <avagin@google.com>
Cc: Joel Granados <joel.granados@kernel.org>
Cc: Thomas Weißschuh <linux@weissschuh.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
---

diff --git a/kernel/ucount.c b/kernel/ucount.c
index f950b5e59d638..86c5f1c0bad90 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -164,8 +164,8 @@ struct ucounts *get_ucounts(struct ucounts *ucounts)
 struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
 	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
-	struct ucounts *ucounts, *new;
 	bool wrapped;
+	struct ucounts *ucounts, *new = NULL;
 
 	spin_lock_irq(&ucounts_lock);
 	ucounts = find_ucounts(ns, uid, hashent);
@@ -182,17 +182,17 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 
 		spin_lock_irq(&ucounts_lock);
 		ucounts = find_ucounts(ns, uid, hashent);
-		if (ucounts) {
-			kfree(new);
-		} else {
+		if (!ucounts) {
 			hlist_add_head(&new->node, hashent);
 			get_user_ns(new->ns);
 			spin_unlock_irq(&ucounts_lock);
 			return new;
 		}
 	}
+
 	wrapped = !get_ucounts_or_wrap(ucounts);
 	spin_unlock_irq(&ucounts_lock);
+	kfree(new);
 	if (wrapped) {
 		put_ucounts(ucounts);
 		return NULL;