From: Alan Stern <stern@rowland.harvard.edu>
To: Luc Maranget <luc.maranget@inria.fr>
Cc: Boqun Feng <boqun.feng@gmail.com>,
Andrea Parri <parri.andrea@gmail.com>,
Jade Alglave <j.alglave@ucl.ac.uk>,
"Paul E. McKenney" <paulmck@kernel.org>,
Kernel development list <linux-kernel@vger.kernel.org>
Subject: More on reader-writer locks
Date: Tue, 25 Feb 2020 16:42:03 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.2002251608290.1485-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20200225130102.wsz3bpyhjmcru7os@yquem.inria.fr>
On Tue, 25 Feb 2020, Luc Maranget wrote:
> Hi,
>
> As far as I can remember I have implemented atomic_add_unless in herd7.
Luc, have you considered whether we can use atomic_add_unless and
cmpxchg to implement reader-writer locks in the LKMM? I don't think we
can handle them the same way we handle ordinary locks now.
Let's say that a lock variable holds 0 if it is unlocked, -1 if it is
write-locked, and a positive value if it is read-locked (the value is
the number of read locks currently in effect). Then operations like
write_lock, write_trylock, and so on could all be modeled using
variants of atomic_add_unless, atomic_dec, and cmpxchg.
But will that work if the reads-from relation is computed by the cat
code in lock.cat? I suspect it won't.
How would you approach this problem?
Alan
next prev parent reply other threads:[~2020-02-25 21:42 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-14 4:01 [RFC 0/3] tools/memory-model: Add litmus tests for atomic APIs Boqun Feng
2020-02-14 4:01 ` [RFC 1/3] Documentation/locking/atomic: Fix atomic-set litmus test Boqun Feng
2020-02-14 4:01 ` [RFC 2/3] tools/memory-model: Add a litmus test for atomic_set() Boqun Feng
2020-02-14 8:12 ` Andrea Parri
2020-02-14 10:40 ` Boqun Feng
2020-02-25 7:34 ` Boqun Feng
2020-02-25 13:01 ` Luc Maranget
2020-02-25 21:42 ` Alan Stern [this message]
2020-02-26 9:46 ` More on reader-writer locks Luc Maranget
2020-02-26 2:51 ` [RFC 2/3] tools/memory-model: Add a litmus test for atomic_set() Boqun Feng
2020-02-14 15:47 ` Alan Stern
2020-02-14 23:52 ` Boqun Feng
2020-02-17 11:02 ` Peter Zijlstra
2020-02-14 4:01 ` [RFC 3/3] tools/memory-model: Add litmus test for RMW + smp_mb__after_atomic() Boqun Feng
2020-02-14 6:15 ` Boqun Feng
2020-02-14 8:18 ` Andrea Parri
2020-02-14 8:20 ` Boqun Feng
2020-02-14 15:58 ` Alan Stern
2020-02-15 0:09 ` Boqun Feng
2020-02-14 9:55 ` [RFC 0/3] tools/memory-model: Add litmus tests for atomic APIs Peter Zijlstra
2020-02-14 10:20 ` Paul E. McKenney
2020-02-14 15:27 ` Alan Stern
2020-02-14 23:39 ` Boqun Feng
2020-02-15 15:25 ` Paul E. McKenney
2020-02-16 5:43 ` Boqun Feng
2020-02-16 12:06 ` Paul E. McKenney
2020-02-16 16:16 ` Alan Stern
2020-02-17 1:27 ` Boqun Feng
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