From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753788AbeDAQmk (ORCPT ); Sun, 1 Apr 2018 12:42:40 -0400 Received: from mail-wm0-f66.google.com ([74.125.82.66]:55048 "EHLO mail-wm0-f66.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1753730AbeDAQmg (ORCPT ); Sun, 1 Apr 2018 12:42:36 -0400 X-Google-Smtp-Source: AIpwx4/qQnd4UZ1UNwIPiHGaheeBT4dq6uZ9m2w34Wctt4ylKblDtJz7la9v7KKy8cp5DppBEJuG4A== From: Andrea Parri To: paulmck@linux.vnet.ibm.com, Ingo Molnar , Peter Zijlstra Cc: linux-kernel@vger.kernel.org, Andrea Parri , Andrea Parri , Alan Stern , Will Deacon , Boqun Feng , Nicholas Piggin , David Howells , Jade Alglave , Luc Maranget , Akira Yokosawa Subject: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() Date: Sun, 1 Apr 2018 18:41:50 +0200 Message-Id: <1522600912-6208-2-git-send-email-andrea.parri@amarulasolutions.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1522600912-6208-1-git-send-email-andrea.parri@amarulasolutions.com> References: <1522600912-6208-1-git-send-email-andrea.parri@amarulasolutions.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org There appeared to be a certain, recurrent uncertainty concerning the semantics of spin_is_locked(), likely a consequence of the fact that this semantics remains undocumented or that it has been historically linked to the (likewise unclear) semantics of spin_unlock_wait(). A recent auditing [1] of the callers of the primitive confirmed that none of them are relying on particular ordering guarantees; document this semantics by adding a docbook header to spin_is_locked(). [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 Signed-off-by: Andrea Parri Cc: Alan Stern Cc: Will Deacon Cc: Peter Zijlstra Cc: Boqun Feng Cc: Nicholas Piggin Cc: David Howells Cc: Jade Alglave Cc: Luc Maranget Cc: "Paul E. McKenney" Cc: Akira Yokosawa Cc: Ingo Molnar --- include/linux/spinlock.h | 11 +++++++++++ 1 file changed, 11 insertions(+) diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index 4894d322d2584..2639fdc9a916c 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -380,6 +380,17 @@ static __always_inline int spin_trylock_irq(spinlock_t *lock) raw_spin_trylock_irqsave(spinlock_check(lock), flags); \ }) +/** + * spin_is_locked() - Check whether a spinlock is locked. + * @lock: Pointer to the spinlock. + * + * This function is NOT required to provide any memory ordering + * guarantees; it could be used for debugging purposes or, when + * additional synchronization is needed, accompanied with other + * constructs (memory barriers) enforcing the synchronization. + * + * Return: 1, if @lock is (found to be) locked; 0, otherwise. + */ static __always_inline int spin_is_locked(spinlock_t *lock) { return raw_spin_is_locked(&lock->rlock); -- 2.7.4