From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752311AbeEOG0f (ORCPT ); Tue, 15 May 2018 02:26:35 -0400 Received: from terminus.zytor.com ([198.137.202.136]:43785 "EHLO terminus.zytor.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752097AbeEOG0d (ORCPT ); Tue, 15 May 2018 02:26:33 -0400 Date: Mon, 14 May 2018 23:25:49 -0700 From: tip-bot for Andrea Parri Message-ID: Cc: torvalds@linux-foundation.org, peterz@infradead.org, j.alglave@ucl.ac.uk, dhowells@redhat.com, andrea.parri@amarulasolutions.com, will.deacon@arm.com, akiyks@gmail.com, npiggin@gmail.com, akpm@linux-foundation.org, paulmck@linux.vnet.ibm.com, stern@rowland.harvard.edu, hpa@zytor.com, boqun.feng@gmail.com, mingo@kernel.org, luc.maranget@inria.fr, tglx@linutronix.de, linux-kernel@vger.kernel.org, rdunlap@infradead.org Reply-To: will.deacon@arm.com, andrea.parri@amarulasolutions.com, akiyks@gmail.com, npiggin@gmail.com, j.alglave@ucl.ac.uk, torvalds@linux-foundation.org, peterz@infradead.org, dhowells@redhat.com, tglx@linutronix.de, luc.maranget@inria.fr, mingo@kernel.org, linux-kernel@vger.kernel.org, rdunlap@infradead.org, paulmck@linux.vnet.ibm.com, akpm@linux-foundation.org, hpa@zytor.com, stern@rowland.harvard.edu, boqun.feng@gmail.com In-Reply-To: <1526338889-7003-1-git-send-email-paulmck@linux.vnet.ibm.com> References: <1526338889-7003-1-git-send-email-paulmck@linux.vnet.ibm.com> To: linux-tip-commits@vger.kernel.org Subject: [tip:locking/core] locking/spinlocks: Document the semantics of spin_is_locked() Git-Commit-ID: b7e4aadef28f217de8907eec60a964328797a2be X-Mailer: tip-git-log-daemon Robot-ID: Robot-Unsubscribe: Contact to get blacklisted from these emails MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Content-Type: text/plain; charset=UTF-8 Content-Disposition: inline Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Commit-ID: b7e4aadef28f217de8907eec60a964328797a2be Gitweb: https://git.kernel.org/tip/b7e4aadef28f217de8907eec60a964328797a2be Author: Andrea Parri AuthorDate: Mon, 14 May 2018 16:01:27 -0700 Committer: Ingo Molnar CommitDate: Tue, 15 May 2018 08:11:15 +0200 locking/spinlocks: Document the semantics of spin_is_locked() 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(). Also, describe behaviors specific to certain CONFIG_SMP=n builds. [1] https://marc.info/?l=linux-kernel&m=151981440005264&w=2 https://marc.info/?l=linux-kernel&m=152042843808540&w=2 https://marc.info/?l=linux-kernel&m=152043346110262&w=2 Co-Developed-by: Andrea Parri Co-Developed-by: Alan Stern Co-Developed-by: David Howells Signed-off-by: Andrea Parri Signed-off-by: Alan Stern Signed-off-by: David Howells Signed-off-by: Paul E. McKenney Acked-by: Randy Dunlap Cc: Akira Yokosawa Cc: Andrew Morton Cc: Boqun Feng Cc: Jade Alglave Cc: Linus Torvalds Cc: Luc Maranget Cc: Nicholas Piggin Cc: Peter Zijlstra Cc: Thomas Gleixner Cc: Will Deacon Cc: linux-arch@vger.kernel.org Cc: parri.andrea@gmail.com Link: http://lkml.kernel.org/r/1526338889-7003-1-git-send-email-paulmck@linux.vnet.ibm.com Signed-off-by: Ingo Molnar --- include/linux/spinlock.h | 18 ++++++++++++++++++ 1 file changed, 18 insertions(+) diff --git a/include/linux/spinlock.h b/include/linux/spinlock.h index 4894d322d258..1e8a46435838 100644 --- a/include/linux/spinlock.h +++ b/include/linux/spinlock.h @@ -380,6 +380,24 @@ 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. + * + * Returns: 1 if @lock is locked, 0 otherwise. + * + * Note that the function only tells you that the spinlock is + * seen to be locked, not that it is locked on your CPU. + * + * Further, on CONFIG_SMP=n builds with CONFIG_DEBUG_SPINLOCK=n, + * the return value is always 0 (see include/linux/spinlock_up.h). + * Therefore you should not rely heavily on the return value. + */ static __always_inline int spin_is_locked(spinlock_t *lock) { return raw_spin_is_locked(&lock->rlock);