From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <longman@redhat.com>
Cc: Ingo Molnar <mingo@redhat.com>, Will Deacon <will.deacon@arm.com>,
Thomas Gleixner <tglx@linutronix.de>,
Borislav Petkov <bp@alien8.de>, "H. Peter Anvin" <hpa@zytor.com>,
linux-kernel@vger.kernel.org, x86@kernel.org,
Davidlohr Bueso <dave@stgolabs.net>,
Linus Torvalds <torvalds@linux-foundation.org>,
Tim Chen <tim.c.chen@linux.intel.com>,
huang ying <huang.ying.caritas@gmail.com>
Subject: Re: [PATCH-tip v7 12/20] locking/rwsem: Clarify usage of owner's nonspinaable bit
Date: Fri, 3 May 2019 17:21:25 +0200 [thread overview]
Message-ID: <20190503152125.GH2623@hirez.programming.kicks-ass.net> (raw)
In-Reply-To: <20190428212557.13482-13-longman@redhat.com>
On Sun, Apr 28, 2019 at 05:25:49PM -0400, Waiman Long wrote:
> Bit 1 of sem->owner (RWSEM_ANONYMOUSLY_OWNED) is used to designate an
> anonymous owner - readers or an anonymous writer. The setting of this
> anonymous bit is used as an indicator that optimistic spinning cannot
> be done on this rwsem.
>
> With the upcoming reader optimistic spinning patches, a reader-owned
> rwsem can be spinned on for a limit period of time. We still need
> this bit to indicate a rwsem is nonspinnable, but not setting this
> bit loses its meaning that the owner is known. So rename the bit
> to RWSEM_NONSPINNABLE to clarify its meaning.
>
> This patch also fixes a DEBUG_RWSEMS_WARN_ON() bug in __up_write().
>
> Signed-off-by: Waiman Long <longman@redhat.com>
> ---
> include/linux/rwsem.h | 2 +-
> kernel/locking/rwsem.c | 43 +++++++++++++++++++++---------------------
> 2 files changed, 22 insertions(+), 23 deletions(-)
>
> diff --git a/include/linux/rwsem.h b/include/linux/rwsem.h
> index 148983e21d47..bb76e82398b2 100644
> --- a/include/linux/rwsem.h
> +++ b/include/linux/rwsem.h
> @@ -50,7 +50,7 @@ struct rw_semaphore {
> };
>
> /*
> - * Setting bit 1 of the owner field but not bit 0 will indicate
> + * Setting all bits of the owner field except bit 0 will indicate
> * that the rwsem is writer-owned with an unknown owner.
> */
> #define RWSEM_OWNER_UNKNOWN ((struct task_struct *)-2L)
As you know, I'm trying to kill that :-)
next prev parent reply other threads:[~2019-05-03 15:21 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-04-28 21:25 [PATCH-tip v7 00/20] locking/rwsem: Rwsem rearchitecture part 2 Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 01/20] locking/rwsem: Prevent decrement of reader count before increment Waiman Long
2019-05-03 12:06 ` Peter Zijlstra
2019-05-03 13:32 ` Waiman Long
2019-05-07 7:07 ` [tip:locking/urgent] " tip-bot for Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 02/20] locking/rwsem: Make owner available even if !CONFIG_RWSEM_SPIN_ON_OWNER Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 03/20] locking/rwsem: Remove rwsem_wake() wakeup optimization Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 04/20] locking/rwsem: Implement a new locking scheme Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 05/20] locking/rwsem: Merge rwsem.h and rwsem-xadd.c into rwsem.c Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 06/20] locking/rwsem: Code cleanup after files merging Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 07/20] locking/rwsem: Make rwsem_spin_on_owner() return owner state Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 08/20] locking/rwsem: Implement lock handoff to prevent lock starvation Waiman Long
2019-05-03 13:10 ` Peter Zijlstra
2019-05-03 13:57 ` Waiman Long
2019-05-03 14:37 ` David Laight
2019-04-28 21:25 ` [PATCH-tip v7 09/20] locking/rwsem: Always release wait_lock before waking up tasks Waiman Long
2019-05-03 13:37 ` Peter Zijlstra
2019-05-03 13:56 ` Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 10/20] locking/rwsem: More optimal RT task handling of null owner Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 11/20] locking/rwsem: Wake up almost all readers in wait queue Waiman Long
2019-05-03 16:51 ` Peter Zijlstra
2019-05-03 17:15 ` Waiman Long
2019-05-06 11:49 ` Peter Zijlstra
2019-04-28 21:25 ` [PATCH-tip v7 12/20] locking/rwsem: Clarify usage of owner's nonspinaable bit Waiman Long
2019-05-03 15:21 ` Peter Zijlstra [this message]
2019-05-03 15:26 ` Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 13/20] locking/rwsem: Enable readers spinning on writer Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 14/20] locking/rwsem: Enable time-based spinning on reader-owned rwsem Waiman Long
2019-05-06 15:47 ` Peter Zijlstra
2019-04-28 21:25 ` [PATCH-tip v7 15/20] locking/rwsem: Adaptive disabling of reader optimistic spinning Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 16/20] locking/rwsem: Add more rwsem owner access helpers Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 17/20] locking/rwsem: Guard against making count negative Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 18/20] locking/rwsem: Merge owner into count on x86-64 Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 19/20] locking/rwsem: Remove redundant computation of writer lock word Waiman Long
2019-04-28 21:25 ` [PATCH-tip v7 20/20] locking/rwsem: Disable preemption in down_read*() if owner in count Waiman Long
2019-04-28 22:46 ` [PATCH-tip v7 00/20] locking/rwsem: Rwsem rearchitecture part 2 Linus Torvalds
2019-04-28 23:12 ` Waiman Long
2019-04-28 23:19 ` Waiman Long
2019-04-29 0:10 ` Linus Torvalds
2019-04-29 0:27 ` Waiman Long
2019-04-29 2:41 ` Linus Torvalds
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