Received-SPF: pass (google.com: best guess record for domain of linux-kernel-owner@vger.kernel.org designates 209.132.180.67 as permitted sender) client-ip=209.132.180.67;
MIME-Version: 1.0
References: <20190513091203.7299-1-duyuyang@gmail.com> <20190513091203.7299-2-duyuyang@gmail.com>
 <20190513114504.GR2623@hirez.programming.kicks-ass.net>
In-Reply-To: <20190513114504.GR2623@hirez.programming.kicks-ass.net>
From:   Yuyang Du <duyuyang@gmail.com>
Date:   Tue, 14 May 2019 09:31:48 +0800
Message-ID: <CAHttsrYf_SSEHwPZRqs2KGznPgC9Je3dPOft1bwZ5pYC5R0xUg@mail.gmail.com>
Subject: Re: [PATCH 01/17] locking/lockdep: Add lock type enum to explicitly
 specify read or write locks
To:     Peter Zijlstra <peterz@infradead.org>
Cc:     will.deacon@arm.com, Ingo Molnar <mingo@kernel.org>,
        Bart Van Assche <bvanassche@acm.org>, ming.lei@redhat.com,
        Frederic Weisbecker <frederic@kernel.org>, tglx@linutronix.de,
        Boqun Feng <boqun.feng@gmail.com>,
        LKML <linux-kernel@vger.kernel.org>
Content-Type: text/plain; charset="UTF-8"
Sender: linux-kernel-owner@vger.kernel.org
Precedence: bulk

Thanks for review.

On Mon, 13 May 2019 at 19:45, Peter Zijlstra <peterz@infradead.org> wrote:
>
> On Mon, May 13, 2019 at 05:11:47PM +0800, Yuyang Du wrote:
> > + * Note that we have an assumption that a lock class cannot ever be both
> > + * read and recursive-read.
>
> We have such locks in the kernel... see:
>
>   kernel/qrwlock.c:queued_read_lock_slowpath()
>
> And yes, that is somewhat unfortunate, but hard to get rid of due to
> hysterical raisins.

That is ok, then LOCK_TYPE_RECURSIVE has to be 3 such that
LOCK_TYPE_RECURSIVE & LOCK_TYPE_READ != 0. I thought to do this in the
first place without assuming. Anyway, it is better to know.

And I guess in a task:

(1) read(X);
    recursive_read(x);      /* this is ok ? */

(2) recursive_read(x);
    read(x)      /* not ok ? */

Either way, very small change may need to be made.