linux-kernel - Re: [PATCH-tip v2 02/10] locking/rwsem: Move owner setting code from rwsem.c to rwsem.h

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Message-ID: <20190221141525.GF12696@fuggles.cambridge.arm.com>
Date:   Thu, 21 Feb 2019 14:15:25 +0000
From:   Will Deacon <will.deacon@....com>
To:     Waiman Long <longman@...hat.com>
Cc:     Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, x86@...nel.org,
        Arnd Bergmann <arnd@...db.de>, Borislav Petkov <bp@...en8.de>,
        "H. Peter Anvin" <hpa@...or.com>,
        Davidlohr Bueso <dave@...olabs.net>,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Tim Chen <tim.c.chen@...ux.intel.com>
Subject: Re: [PATCH-tip v2 02/10] locking/rwsem: Move owner setting code from
 rwsem.c to rwsem.h

Hi Waiman,

On Fri, Feb 15, 2019 at 03:50:02PM -0500, Waiman Long wrote:
> Moves all the owner setting code closer to the rwsem-xadd fast paths
> directly within rwsem.h file.
> 
> For __down_read() and __down_read_killable(), it is assumed that
> rwsem will be marked as reader-owned when the functions return. That
> is currently true except in the transient case that the waiter queue
> just becomes empty. So a rwsem_set_reader_owned() call is added for
> this case.

Sorry, but I'm having a really hard time understanding the paragraph
above. You make it sound like you're fixing a bug here, but that doesn't
appear to be the case. Please can you elaborate?

> The __rwsem_set_reader_owned() call in __rwsem_mark_wake()
> is now necessary.
> 
> Signed-off-by: Waiman Long <longman@...hat.com>
> ---
>  kernel/locking/rwsem-xadd.c |  6 +++---
>  kernel/locking/rwsem.c      | 19 ++-----------------
>  kernel/locking/rwsem.h      | 17 +++++++++++++++--
>  3 files changed, 20 insertions(+), 22 deletions(-)

I personally find the existing code easier to read, but I don't know if
that's just because I'm used to it...

Will