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From: Yuyang Du <duyuyang@gmail.com>
To: Boqun Feng <boqun.feng@gmail.com>
Cc: Peter Zijlstra <peterz@infradead.org>,
	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, paulmck@linux.ibm.com,
	LKML <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v2 11/17] locking/lockdep: Adjust lockdep selftest cases
Date: Thu, 30 May 2019 15:37:50 +0800	[thread overview]
Message-ID: <CAHttsrZ962Gw_6OA6J6GEhAx06yV70B5PEzqGEaYGDNSy57-3A@mail.gmail.com> (raw)
In-Reply-To: <20190529114451.GA12812@tardis>

Thanks for review.

On Wed, 29 May 2019 at 19:44, Boqun Feng <boqun.feng@gmail.com> wrote:
>
> > @@ -424,7 +424,7 @@ static void rwsem_ABBA2(void)
> >       ML(Y1);
> >       RSL(X1);
> >       RSU(X1);
> > -     MU(Y1); // should fail
> > +     MU(Y1); // should NOT fail
>
> I'm afraid you get this wrong ;-) reader of rwsem is non-recursive if I
> understand correctly, so case like:
>
>         Task 0                  Task 1
>
>         down_read(A);
>                                 mutex_lock(B);
>
>                                 down_read(A);
>         mutex_lock(B);
>
> can be a deadlock, if we consider a third independent task:
>
>         Task 0                  Task 1                  Task 2
>
>         down_read(A);
>                                 mutex_lock(B);
>                                                         down_write(A);
>                                 down_read(A);
>         mutex_lock(B);
>
> in this case, Task 1 can not get it's lock for A, therefore, deadlock.

Well, yes. This situation is damn counterintuitive and looks
suboptimal, but I guess I can understand why this is done so. It is a
shame read locks are not 100% concurrent. I wish I were bright enough
to have figured this out on my own.

Ok, now this perhaps can be easily remedied. it is merely a matter
that finally I can set straight the lock exclusiveness table, and then
from there the only change seems to be now only recursive-read locks
are no deadlock.

Thanks,
Yuyang

  reply	other threads:[~2019-05-30  7:38 UTC|newest]

Thread overview: 21+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-05-16  7:59 [PATCH v2 00/17] Support for read-write lock deadlock detection Yuyang Du
2019-05-16  7:59 ` [PATCH v2 01/17] locking/lockdep: Add lock type enum to explicitly specify read or write locks Yuyang Du
2019-05-16  8:00 ` [PATCH v2 02/17] locking/lockdep: Add read-write type for dependency Yuyang Du
2019-05-29 11:37   ` Boqun Feng
2019-05-16  8:00 ` [PATCH v2 03/17] locking/lockdep: Add helper functions to operate on the searched path Yuyang Du
2019-05-16  8:00 ` [PATCH v2 04/17] locking/lockdep: Update direct dependency's read-write type if it exists Yuyang Du
2019-05-16  8:00 ` [PATCH v2 05/17] locking/lockdep: Rename deadlock check functions Yuyang Du
2019-05-16  8:00 ` [PATCH v2 06/17] locking/lockdep: Adjust BFS algorithm to support multiple matches Yuyang Du
2019-05-16  8:00 ` [PATCH v2 07/17] locking/lockdep: Introduce mark_lock_unaccessed() Yuyang Du
2019-05-16  8:00 ` [PATCH v2 08/17] locking/lockdep: Introduce chain_hlocks_type for held lock's read-write type Yuyang Du
2019-05-16  8:00 ` [PATCH v2 09/17] locking/lockdep: Hash held lock's read-write type into chain key Yuyang Du
2019-05-16  8:00 ` [PATCH v2 10/17] locking/lockdep: Support read-write lock's deadlock detection Yuyang Du
2019-05-16  8:00 ` [PATCH v2 11/17] locking/lockdep: Adjust lockdep selftest cases Yuyang Du
2019-05-29 11:44   ` Boqun Feng
2019-05-30  7:37     ` Yuyang Du [this message]
2019-05-16  8:00 ` [PATCH v2 12/17] locking/lockdep: Remove useless lock type assignment Yuyang Du
2019-05-16  8:00 ` [PATCH v2 13/17] locking/lockdep: Add nest lock type Yuyang Du
2019-05-16  8:00 ` [PATCH v2 14/17] locking/lockdep: Support recursive read locks Yuyang Du
2019-05-16  8:00 ` [PATCH v2 15/17] locking/lockdep: Adjust selftest case for recursive read lock Yuyang Du
2019-05-16  8:00 ` [PATCH v2 16/17] locking/lockdep: Add more lockdep selftest cases Yuyang Du
2019-05-16  8:00 ` [PATCH v2 17/17] locking/lockdep: Remove irq-safe to irq-unsafe read check Yuyang Du

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