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From: David Howells <dhowells@redhat.com>
To: Andrea Parri <andrea.parri@amarulasolutions.com>
Cc: dhowells@redhat.com, paulmck@linux.vnet.ibm.com,
	Ingo Molnar <mingo@redhat.com>,
	Peter Zijlstra <peterz@infradead.org>,
	linux-kernel@vger.kernel.org,
	Andrea Parri <parri.andrea@gmail.com>,
	Alan Stern <stern@rowland.harvard.edu>,
	Will Deacon <will.deacon@arm.com>,
	Boqun Feng <boqun.feng@gmail.com>,
	Nicholas Piggin <npiggin@gmail.com>,
	Jade Alglave <j.alglave@ucl.ac.uk>,
	Luc Maranget <luc.maranget@inria.fr>,
	Akira Yokosawa <akiyks@gmail.com>
Subject: Re: [PATCH v2 1/3] locking: Document the semantics of spin_is_locked()
Date: Tue, 03 Apr 2018 13:49:09 +0100	[thread overview]
Message-ID: <29562.1522759749@warthog.procyon.org.uk> (raw)
In-Reply-To: <1522600912-6208-2-git-send-email-andrea.parri@amarulasolutions.com>

Andrea Parri <andrea.parri@amarulasolutions.com> wrote:

> +/**
> + * 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.

It's more complicated than that.  This function is dangerous and should be
used with extreme care.  In the case where CONFIG_SMP=n the value is locked
one way or the other and it might be the wrong way.

David

  parent reply	other threads:[~2018-04-03 12:49 UTC|newest]

Thread overview: 33+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2018-04-01 16:41 [PATCH v3 0/3] Changes, clean-ups and documentation for spin_is_locked() Andrea Parri
2018-04-01 16:41 ` [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() Andrea Parri
2018-04-02 14:03   ` Alan Stern
2018-04-02 19:35     ` Paul E. McKenney
2018-04-06 19:47   ` [PATCH v4 " Andrea Parri
2018-04-06 21:00     ` Paul E. McKenney
2018-04-06 21:01     ` Randy Dunlap
2018-04-06 21:07       ` Paul E. McKenney
2018-04-06 21:08         ` Randy Dunlap
2018-04-06 21:58           ` Andrea Parri
2018-04-08 21:14             ` Paul E. McKenney
2018-04-08 21:32               ` Randy Dunlap
2018-04-08 22:00                 ` Paul E. McKenney
2018-04-01 16:41 ` [PATCH v3 2/3] arm64: Remove smp_mb() from arch_spin_is_locked() Andrea Parri
2018-04-01 16:41 ` [PATCH v3 3/3] locking: Clean up comment and #ifndef for {,queued_}spin_is_locked() Andrea Parri
2018-04-01 18:24 ` [PATCH v3 0/3] Changes, clean-ups and documentation for spin_is_locked() Paul E. McKenney
2018-04-03 12:49 ` David Howells [this message]
2018-04-03 13:35   ` [PATCH v2 1/3] locking: Document the semantics of spin_is_locked() Andrea Parri
2018-04-03 13:52   ` David Howells
2018-04-03 14:07     ` Andrea Parri
2018-04-03 14:17     ` Paul E. McKenney
2018-04-03 14:43       ` Peter Zijlstra
2018-04-03 15:03         ` Paul E. McKenney
2018-04-03 16:11           ` Paul E. McKenney
2018-04-03 15:23     ` David Howells
2018-04-03 19:31       ` Andrea Parri
2018-04-03 20:04         ` Alan Stern
2018-04-03 21:43           ` David Howells
2018-04-03 21:47             ` Randy Dunlap
2018-04-04 12:47             ` Andrea Parri
2018-04-04 21:22             ` David Howells
2018-04-05  7:47   ` Christoph Hellwig
2018-04-05  8:56     ` Andrea Parri

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