The patch titled
Subject: ucount: replace get_ucounts_or_wrap() with atomic_inc_not_zero()
has been added to the -mm mm-nonmm-unstable branch. Its filename is
ucount-replace-get_ucounts_or_wrap-with-atomic_inc_not_zero.patch
This patch will shortly appear at
https://git.kernel.org/pub/scm/linux/kernel/git/akpm/25-new.git/tree/patches/ucount-replace-get_ucounts_or_wrap-with-atomic_inc_not_zero.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: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Subject: ucount: replace get_ucounts_or_wrap() with atomic_inc_not_zero()
Date: Mon, 3 Feb 2025 16:05:23 +0100
get_ucounts_or_wrap() increments the counter and if the counter is
negative then it decrements it again in order to reset the previous
increment. This statement can be replaced with atomic_inc_not_zero() to
only increment the counter if it is not yet 0.
This simplifies the get function because the put (if the get failed) can
be removed. atomic_inc_not_zero() is implement as a cmpxchg() loop which
can be repeated several times if another get/put is performed in parallel.
This will be optimized later.
Increment the reference counter only if not yet dropped to zero.
Link: https://lkml.kernel.org/r/20250203150525.456525-3-bigeasy@xxxxxxxxxxxxx
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@xxxxxxxxxxxxx>
Reviewed-by: Paul E. McKenney <paulmck@xxxxxxxxxx>
Cc: Acked-by:Thomas Gleixner <tglx@xxxxxxxxxxxxx>
Cc: Boqun Feng <boqun.feng@xxxxxxxxx>
Cc: Joel Fernandes <joel@xxxxxxxxxxxxxxxxx>
Cc: Josh Triplett <josh@xxxxxxxxxxxxxxxx>
Cc: Lai jiangshan <jiangshanlai@xxxxxxxxx>
Cc: Mathieu Desnoyers <mathieu.desnoyers@xxxxxxxxxxxx>
Cc: Mengen Sun <mengensun@xxxxxxxxxxx>
Cc: Steven Rostedt <rostedt@xxxxxxxxxxx>
Cc: "Uladzislau Rezki (Sony)" <urezki@xxxxxxxxx>
Cc: YueHong Wu <yuehongwu@xxxxxxxxxxx>
Cc: Zqiang <qiang.zhang1211@xxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
kernel/ucount.c | 24 ++++++------------------
1 file changed, 6 insertions(+), 18 deletions(-)
--- a/kernel/ucount.c~ucount-replace-get_ucounts_or_wrap-with-atomic_inc_not_zero
+++ a/kernel/ucount.c
@@ -146,25 +146,16 @@ static void hlist_add_ucounts(struct uco
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 (!get_ucounts_or_wrap(ucounts)) {
- put_ucounts(ucounts);
- ucounts = NULL;
- }
- return ucounts;
+ if (atomic_inc_not_zero(&ucounts->count))
+ return ucounts;
+ return NULL;
}
struct ucounts *alloc_ucounts(struct user_namespace *ns, kuid_t uid)
{
struct hlist_head *hashent = ucounts_hashentry(ns, uid);
- bool wrapped;
struct ucounts *ucounts, *new = NULL;
spin_lock_irq(&ucounts_lock);
@@ -189,14 +180,11 @@ struct ucounts *alloc_ucounts(struct use
return new;
}
}
-
- wrapped = !get_ucounts_or_wrap(ucounts);
+ if (!atomic_inc_not_zero(&ucounts->count))
+ ucounts = NULL;
spin_unlock_irq(&ucounts_lock);
kfree(new);
- if (wrapped) {
- put_ucounts(ucounts);
- return NULL;
- }
+
return ucounts;
}
_
Patches currently in -mm which might be from bigeasy@xxxxxxxxxxxxx are
rcu-provide-a-static-initializer-for-hlist_nulls_head.patch
ucount-replace-get_ucounts_or_wrap-with-atomic_inc_not_zero.patch
ucount-use-rcu-for-ucounts-lookups.patch
ucount-use-rcuref_t-for-reference-counting.patch
