linux-kernel - [PATCH 0/4] ucount: Simplify refcounting with rcuref

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Message-ID: <20250203150525.456525-1-bigeasy@linutronix.de>
Date: Mon,  3 Feb 2025 16:05:21 +0100
From: Sebastian Andrzej Siewior <bigeasy@...utronix.de>
To: linux-kernel@...r.kernel.org,
	rcu@...r.kernel.org
Cc: Andrew Morton <akpm@...ux-foundation.org>,
	MengEn Sun <mengensun@...cent.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	YueHong Wu <yuehongwu@...cent.com>,
	"Paul E. McKenney" <paulmck@...nel.org>,
	Joel Fernandes <joel@...lfernandes.org>,
	Josh Triplett <josh@...htriplett.org>,
	Boqun Feng <boqun.feng@...il.com>,
	Uladzislau Rezki <urezki@...il.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>,
	Lai Jiangshan <jiangshanlai@...il.com>,
	Zqiang <qiang.zhang1211@...il.com>,
	Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: [PATCH 0/4] ucount: Simplify refcounting with rcuref_t.

I noticed that the atomic_dec_and_lock_irqsave() in put_ucounts() loops
sometimes even during boot. Something like 2-3 iterations but still.
This series replaces the refcounting with rcuref_t and adds a RCU
lookup.
This allows a lockless lookup in alloc_ucounts() if the entry is
available and a cmpxchg()less put of the item.

Patch #1 adds HLIST_NULLS_HEAD_INIT for which I added the RCU folks.

Sebastian

Sebastian Andrzej Siewior (4):
  rcu: Provide a static initializer for hlist_nulls_head.
  ucount: Replace get_ucounts_or_wrap() with atomic_inc_not_zero().
  ucount: Use RCU for ucounts lookups.
  ucount: Use rcuref_t for reference counting.

 include/linux/list_nulls.h     |  1 +
 include/linux/user_namespace.h | 15 ++++--
 kernel/ucount.c                | 97 +++++++++++++++-------------------
 3 files changed, 55 insertions(+), 58 deletions(-)

-- 
2.47.2