+ ucounts-move-kfree-out-of-critical-zone-protected-by-ucounts_lock.patch added to mm-nonmm-unstable branch

[Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>]

The patch titled
     Subject: ucounts: move kfree() out of critical zone protected by ucounts_lock
has been added to the -mm mm-nonmm-unstable branch.  Its filename is
     ucounts-move-kfree-out-of-critical-zone-protected-by-ucounts_lock.patch

This patch will shortly appear at
     https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ucounts-move-kfree-out-of-critical-zone-protected-by-ucounts_lock.patch

This patch will later appear in the mm-nonmm-unstable branch at
    git://git.kernel.org/pub/scm/linux/kernel/git/akpm/mm

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------------------------------------------------------
From: MengEn Sun <mengensun@xxxxxxxxxxx>
Subject: ucounts: move kfree() out of critical zone protected by ucounts_lock
Date: Mon, 2 Dec 2024 22:32:45 +0800

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/1733149965-749-1-git-send-email-mengensun@xxxxxxxxxxx
Signed-off-by: MengEn Sun <mengensun@xxxxxxxxxxx>
Reviewed-by: YueHong Wu <yuehongwu@xxxxxxxxxxx>
Cc: Andrei Vagin <avagin@xxxxxxxxxx>
Cc: Joel Granados <joel.granados@xxxxxxxxxx>
Cc: Thomas WeiÃ?schuh <linux@xxxxxxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---

 kernel/ucount.c |    8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

--- a/kernel/ucount.c~ucounts-move-kfree-out-of-critical-zone-protected-by-ucounts_lock
+++ a/kernel/ucount.c
@@ -164,8 +164,8 @@ struct ucounts *get_ucounts(struct ucoun
 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 use
 
 		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;
_

Patches currently in -mm which might be from mengensun@xxxxxxxxxxx are

ucounts-move-kfree-out-of-critical-zone-protected-by-ucounts_lock.patch