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Date: Wed, 4 Apr 2018 14:47:47 +0200
From: Andrea Parri <andrea.parri@...rulasolutions.com>
To: David Howells <dhowells@...hat.com>
Cc: Alan Stern <stern@...land.harvard.edu>, paulmck@...ux.vnet.ibm.com,
Ingo Molnar <mingo@...hat.com>,
Peter Zijlstra <peterz@...radead.org>,
linux-kernel@...r.kernel.org,
Andrea Parri <parri.andrea@...il.com>,
Will Deacon <will.deacon@....com>,
Boqun Feng <boqun.feng@...il.com>,
Nicholas Piggin <npiggin@...il.com>,
Jade Alglave <j.alglave@....ac.uk>,
Luc Maranget <luc.maranget@...ia.fr>,
Akira Yokosawa <akiyks@...il.com>,
Randy Dunlap <rdunlap@...radead.org>
Subject: Re: [PATCH v2 1/3] locking: Document the semantics of
spin_is_locked()
On Tue, Apr 03, 2018 at 10:43:14PM +0100, David Howells wrote:
> Alan Stern <stern@...land.harvard.edu> wrote:
>
> > + * Returns: 1 if @lock is locked, 0 otherwise.
> > + * However, on !CONFIG_SMP builds with !CONFIG_DEBUG_SPINLOCK,
> > + * the return value is always 0 (see include/linux/spinlock_up.h).
> > + * Therefore you should not rely heavily on the return value.
>
> Seems reasonable.
>
> It might also want to include a note that the lock isn't necessarily held by
> your own CPU. I would also use "=n" rather than "!", so maybe something like:
>
> * Returns: 1 if @lock is locked, 0 otherwise.
> *
> * Note that the function only tells you that the CPU 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.
Thank you all for the suggestions. I plan to integrate these in the next
version of the patch, which should also include your Co-developed-by:
Andrea
>
> David
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