From: Matthew Wilcox <willy@infradead.org>
To: Andrew Morton <akpm@linux-foundation.org>
Cc: Sebastian Andrzej Siewior <bigeasy@linutronix.de>,
linux-kernel@vger.kernel.org,
Peter Zijlstra <peterz@infradead.org>,
Ingo Molnar <mingo@kernel.org>,
Steven Rostedt <rostedt@goodmis.org>,
Will Deacon <will@kernel.org>,
Thomas Gleixner <tglx@linutronix.de>,
"Paul E . McKenney" <paulmck@kernel.org>,
Linus Torvalds <torvalds@linux-foundation.org>,
linux-mm@kvack.org
Subject: Re: [PATCH 4/8] mm/swap: Use local_lock for protection
Date: Tue, 19 May 2020 19:17:38 -0700 [thread overview]
Message-ID: <20200520021738.GC16070@bombadil.infradead.org> (raw)
In-Reply-To: <20200519165837.883035d3228c582b9bff1d77@linux-foundation.org>
On Tue, May 19, 2020 at 04:58:37PM -0700, Andrew Morton wrote:
> On Tue, 19 May 2020 22:19:08 +0200 Sebastian Andrzej Siewior <bigeasy@linutronix.de> wrote:
> > + local_lock(swapvec_lock);
>
> It's quite peculiar that these operations appear to be pass-by-value.
> All other locking operations are pass-by-reference - spin_lock(&lock),
> not spin_lock(lock). This is what the eye expects to see and it's
> simply more logical - calling code shouldn't have to "know" that the
> locking operations are implemented as cpp macros. And we'd be in a
> mess if someone tried to convert these to real C functions.
The funny thing is that the documentation gets this right:
+The mapping of local_lock to spinlock_t on PREEMPT_RT kernels has a few
+implications. For example, on a non-PREEMPT_RT kernel the following code
+sequence works as expected::
+
+ local_lock_irq(&local_lock);
+ raw_spin_lock(&lock);
but apparently the implementation changed without the documentation matching.
next prev parent reply other threads:[~2020-05-20 2:17 UTC|newest]
Thread overview: 10+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20200519201912.1564477-1-bigeasy@linutronix.de>
2020-05-19 20:19 ` Sebastian Andrzej Siewior
2020-05-19 23:58 ` Andrew Morton
2020-05-20 2:17 ` Matthew Wilcox [this message]
2020-05-20 10:53 ` Peter Zijlstra
2020-05-19 20:19 ` [PATCH 8/8] mm/zswap: Use local lock to protect per-CPU data Sebastian Andrzej Siewior
2020-05-19 21:46 ` Song Bao Hua
2020-05-20 10:26 ` Sebastian Andrzej Siewior
2020-05-20 11:13 ` Song Bao Hua
2020-05-20 11:57 ` Sebastian Andrzej Siewior
2020-05-20 12:01 ` Song Bao Hua
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