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From: Peter Zijlstra <peterz@infradead.org>
To: Yuyang Du <duyuyang@gmail.com>
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>
Subject: Re: [PATCH 01/17] locking/lockdep: Add lock type enum to explicitly specify read or write locks
Date: Tue, 14 May 2019 14:04:04 +0200	[thread overview]
Message-ID: <20190514120404.GQ2589@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <CAHttsrYf_SSEHwPZRqs2KGznPgC9Je3dPOft1bwZ5pYC5R0xUg@mail.gmail.com>

On Tue, May 14, 2019 at 09:31:48AM +0800, Yuyang Du wrote:
> 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 ? */

Correct, that is the use-case for that 'funny' construct.

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

Indeed, read can block due to a pending writer, while recurise_read will
not suffer like that.

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

OK, excellent.

  reply	other threads:[~2019-05-14 12:04 UTC|newest]

Thread overview: 22+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-13  9:11 [PATCH 00/17] Support for read-write lock deadlock detection Yuyang Du
2019-05-13  9:11 ` [PATCH 01/17] locking/lockdep: Add lock type enum to explicitly specify read or write locks Yuyang Du
2019-05-13 11:45   ` Peter Zijlstra
2019-05-14  1:31     ` Yuyang Du
2019-05-14 12:04       ` Peter Zijlstra [this message]
2019-05-13  9:11 ` [PATCH 02/17] locking/lockdep: Add read-write type for dependency Yuyang Du
2019-05-13  9:11 ` [PATCH 03/17] locking/lockdep: Add helper functions to operate on the searched path Yuyang Du
2019-05-13  9:11 ` [PATCH 04/17] locking/lockdep: Update direct dependency's read-write type if it exists Yuyang Du
2019-05-13  9:11 ` [PATCH 05/17] locking/lockdep: Rename deadlock check functions Yuyang Du
2019-05-13  9:11 ` [PATCH 06/17] locking/lockdep: Adjust BFS algorithm to support multiple matches Yuyang Du
2019-05-13  9:11 ` [PATCH 07/17] locking/lockdep: Introduce mark_lock_unaccessed() Yuyang Du
2019-05-13  9:11 ` [PATCH 08/17] locking/lockdep: Introduce chain_hlocks_type for held lock's read-write type Yuyang Du
2019-05-13  9:11 ` [PATCH 09/17] locking/lockdep: Hash held lock's read-write type into chain key Yuyang Du
2019-05-13  9:11 ` [PATCH 10/17] locking/lockdep: Support read-write lock's deadlock detection Yuyang Du
2019-05-13  9:11 ` [PATCH 11/17] locking/lockdep: Adjust lockdep selftest cases Yuyang Du
2019-05-13  9:11 ` [PATCH 12/17] locking/lockdep: Remove useless lock type assignment Yuyang Du
2019-05-13  9:11 ` [PATCH 13/17] locking/lockdep: Add nest lock type Yuyang Du
2019-05-13  9:12 ` [PATCH 14/17] locking/lockdep: Support recursive read locks Yuyang Du
2019-05-13  9:12 ` [PATCH 15/17] locking/lockdep: Adjust selftest case for recursive read lock Yuyang Du
2019-05-13  9:12 ` [PATCH 16/17] locking/lockdep: Add more lockdep selftest cases Yuyang Du
2019-05-13  9:12 ` [PATCH 17/17] locking/lockdep: Remove irq-safe to irq-unsafe read check Yuyang Du
2019-05-13  9:17 ` [PATCH 00/17] Support for read-write lock deadlock detection Yuyang Du

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