linux-kernel - [PATCH 1/2] ucounts: Move kfree() out of critical zone protected by ucounts

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Message-Id: <1733453842-5773-1-git-send-email-mengensun@tencent.com>
Date: Fri,  6 Dec 2024 10:57:22 +0800
From: mengensun88@...il.com
To: akpm@...ux-foundation.org
Cc: linux@...ssschuh.net,
	joel.granados@...nel.org,
	avagin@...gle.com,
	linux-kernel@...r.kernel.org,
	yuehongwu@...cent.com,
	MengEn Sun <mengensun@...cent.com>
Subject: [PATCH 1/2] ucounts: Move kfree() out of critical zone protected by ucounts_lock

From: MengEn Sun <mengensun@...cent.com>

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.

Reviewed-by: YueHong Wu <yuehongwu@...cent.com>
Signed-off-by: MengEn Sun <mengensun@...cent.com>
---
 kernel/ucount.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index f950b5e5..86c5f1c 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;
-- 
1.8.3.1