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From: Alan Stern <stern@rowland.harvard.edu>
To: Eric Biggers <ebiggers@kernel.org>
Cc: Matthew Wilcox <willy@infradead.org>,
linux-kernel@vger.kernel.org, linux-arch@vger.kernel.org,
"Paul E . McKenney" <paulmck@kernel.org>,
linux-fsdevel@vger.kernel.org, Akira Yokosawa <akiyks@gmail.com>,
Andrea Parri <parri.andrea@gmail.com>,
Boqun Feng <boqun.feng@gmail.com>,
Daniel Lustig <dlustig@nvidia.com>,
"Darrick J . Wong" <darrick.wong@oracle.com>,
Dave Chinner <david@fromorbit.com>,
David Howells <dhowells@redhat.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
Luc Maranget <luc.maranget@inria.fr>,
Nicholas Piggin <npiggin@gmail.com>,
Peter Zijlstra <peterz@infradead.org>,
Will Deacon <will@kernel.org>
Subject: Re: [PATCH] tools/memory-model: document the "one-time init" pattern
Date: Sat, 18 Jul 2020 10:35:02 -0400 [thread overview]
Message-ID: <20200718143502.GC1179836@rowland.harvard.edu> (raw)
In-Reply-To: <20200718052818.GF2183@sol.localdomain>
On Fri, Jul 17, 2020 at 10:28:18PM -0700, Eric Biggers wrote:
> /**
> * INIT_ONCE() - do one-time initialization
> * @done: pointer to a 'bool' flag that tracks whether initialization has been
> * done yet or not. Must be false by default.
> * @mutex: pointer to a mutex to use to synchronize executions of @init_func
> * @init_func: the one-time initialization function
> * @...: additional arguments to pass to @init_func (optional)
> *
> * This is a more general version of DO_ONCE_BLOCKING() which supports
> * non-static data by allowing the user to specify their own 'done' flag and
> * mutex.
> *
> * Return: 0 on success (done or already done), or a negative errno value
> * returned by @init_func.
It might be worth pointing out explicitly that init_func can be called
multiple times, if it returns an error.
> */
> #define INIT_ONCE(done, mutex, init_func, ...) \
> ({ \
> int err = 0; \
> \
> if (!smp_load_acquire(done)) { \
> mutex_lock(mutex); \
> if (!*(done)) { \
> err = init_func(__VA_ARGS__); \
> if (!err) \
> smp_store_release((done), true); \
> } \
> mutex_unlock(mutex); \
> } \
> err; \
> })
If this macro is invoked in multiple places for the same object (which
is not unlikely), there is a distinct risk that people will supply
different mutexes or done variables for the invocations.
IMO a better approach would be to have a macro which, given a variable
name v, generates an actual init_once_v() function. Then code wanting
to use v would call init_once_v() first, with no danger of inconsistent
usage. You can fill in the details...
Alan Stern
next prev parent reply other threads:[~2020-07-18 14:35 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-07-17 4:44 Eric Biggers
2020-07-17 5:49 ` Sedat Dilek
2020-07-17 12:35 ` Matthew Wilcox
2020-07-17 14:26 ` Alan Stern
2020-07-17 17:47 ` Matthew Wilcox
2020-07-17 17:51 ` Alan Stern
2020-07-18 1:02 ` Eric Biggers
2020-07-27 12:51 ` Matthew Wilcox
2020-07-17 21:05 ` Darrick J. Wong
2020-07-18 0:44 ` Darrick J. Wong
2020-07-18 1:38 ` Eric Biggers
2020-07-18 2:13 ` Matthew Wilcox
2020-07-18 5:28 ` Eric Biggers
2020-07-18 14:35 ` Alan Stern [this message]
2020-07-20 2:07 ` Dave Chinner
2020-07-20 9:00 ` Peter Zijlstra
2020-07-27 15:17 ` Alan Stern
2020-07-27 15:28 ` Matthew Wilcox
2020-07-27 16:01 ` Paul E. McKenney
2020-07-27 16:31 ` Alan Stern
2020-07-27 16:59 ` Matthew Wilcox
2020-07-27 19:13 ` Alan Stern
2020-07-17 20:53 ` Darrick J. Wong
2020-07-18 0:58 ` Eric Biggers
2020-07-18 1:25 ` Alan Stern
2020-07-18 1:40 ` Matthew Wilcox
2020-07-18 2:00 ` Dave Chinner
2020-07-18 14:21 ` Alan Stern
2020-07-18 2:00 ` Eric Biggers
2020-07-18 1:42 ` Dave Chinner
2020-07-18 14:08 ` Alan Stern
2020-07-20 1:33 ` Dave Chinner
2020-07-20 14:52 ` Alan Stern
2020-07-20 15:37 ` Darrick J. Wong
2020-07-20 15:39 ` Matthew Wilcox
2020-07-20 16:04 ` Paul E. McKenney
2020-07-20 16:48 ` peterz
2020-07-20 22:06 ` Paul E. McKenney
2020-07-20 16:12 ` Alan Stern
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