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ucount: replace get_ucounts_or_wrap() with atomic_inc_not_zero()

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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@linutronix.de
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Paul E. McKenney <paulmck@kernel.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: Boqun Feng <boqun.feng@gmail.com>
Cc: Joel Fernandes <joel@joelfernandes.org>
Cc: Josh Triplett <josh@joshtriplett.org>
Cc: Lai jiangshan <jiangshanlai@gmail.com>
Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
Cc: Mengen Sun <mengensun@tencent.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: "Uladzislau Rezki (Sony)" <urezki@gmail.com>
Cc: YueHong Wu <yuehongwu@tencent.com>
Cc: Zqiang <qiang.zhang1211@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
This commit is contained in:
Sebastian Andrzej Siewior
2025-02-03 16:05:23 +01:00
committed by Andrew Morton
parent 8c6bbda879
commit 328152e677
1 changed files with 6 additions and 18 deletions
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24
kernel/ucount.c
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@@ -146,25 +146,16 @@ 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 (!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 user_namespace *ns, kuid_t uid)
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;
}