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From:   ebiederm@xmission.com (Eric W. Biederman)
To:     Alexey Gladkov <legion@kernel.org>
Cc:     Rune Kleveland <rune.kleveland@infomedia.dk>,
        Yu Zhao <yuzhao@google.com>,
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Date:   Mon, 18 Oct 2021 12:56:58 -0500
In-Reply-To: <877dearzfo.fsf_-_@disp2133> (Eric W. Biederman's message of
        "Mon, 18 Oct 2021 12:54:35 -0500")
Message-ID: <87pms2qkr9.fsf_-_@disp2133>
User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/26.1 (gnu/linux)
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Content-Type: text/plain
Subject: [PATCH 3/4] ucounts: Add get_ucounts_or_wrap for clarity
Precedence: bulk


Add a helper function get_ucounts_or_wrap that is a trivial
wrapper around atomic_add_negative, that makes it clear
how atomic_add_negative is used in the context of ucounts.

Signed-off-by: "Eric W. Biederman" <ebiederm@xmission.com>
---
 kernel/ucount.c | 14 ++++++++++----
 1 file changed, 10 insertions(+), 4 deletions(-)

diff --git a/kernel/ucount.c b/kernel/ucount.c
index 708d05164a7d..133b6044fda4 100644
--- a/kernel/ucount.c
+++ b/kernel/ucount.c
@@ -150,9 +150,15 @@ static void hlist_add_ucounts(struct ucounts *ucounts)
 	spin_unlock_irq(&ucounts_lock);
 }
 
+static inline bool get_ucounts_or_wrap(struct ucounts *ucounts)
+{
+	/* Returns true on a successful get, false if the count wraps. */
+	return !atomic_add_negative(1, &ucounts->count);
+}
+
 struct ucounts *get_ucounts(struct ucounts *ucounts)
 {
-	if (atomic_add_negative(1, &ucounts->count)) {
+	if (!get_ucounts_or_wrap(ucounts)) {
 		put_ucounts(ucounts);
 		ucounts = NULL;
 	}
@@ -163,7 +169,7 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 {
 	struct hlist_head *hashent = ucounts_hashentry(ns, uid);
 	struct ucounts *ucounts, *new;
-	long overflow;
+	bool wrapped;
 
 	spin_lock_irq(&ucounts_lock);
 	ucounts = find_ucounts(ns, uid, hashent);
@@ -188,9 +194,9 @@ struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
 			return new;
 		}
 	}
-	overflow = atomic_add_negative(1, &ucounts->count);
+	wrapped = !get_ucounts_or_wrap(ucounts);
 	spin_unlock_irq(&ucounts_lock);
-	if (overflow) {
+	if (wrapped) {
 		put_ucounts(ucounts);
 		return NULL;
 	}
-- 
2.20.1