lists.openwall.net   lists  /  announce  owl-users  owl-dev  john-users  john-dev  passwdqc-users  yescrypt  popa3d-users  /  oss-security  kernel-hardening  musl  sabotage  tlsify  passwords  /  crypt-dev  xvendor  /  Bugtraq  Full-Disclosure  linux-kernel  linux-netdev  linux-ext4  linux-hardening  linux-cve-announce  PHC 
Open Source and information security mailing list archives
 
Hash Suite: Windows password security audit tool. GUI, reports in PDF.
[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20180515124532.GA19429@redhat.com>
Date:   Tue, 15 May 2018 14:45:32 +0200
From:   Oleg Nesterov <oleg@...hat.com>
To:     Peter Zijlstra <peterz@...radead.org>
Cc:     Waiman Long <longman@...hat.com>, Ingo Molnar <mingo@...hat.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org,
        Davidlohr Bueso <dave@...olabs.net>,
        "Theodore Y. Ts'o" <tytso@....edu>,
        Amir Goldstein <amir73il@...il.com>, Jan Kara <jack@...e.cz>
Subject: Re: [RFC PATCH v2 2/2] locking/percpu-rwsem: Mark rwsem as
 non-spinnable in percpu_rwsem_release()

On 05/15, Peter Zijlstra wrote:
>
> > > Afaict the whole .owner=NULL thing in release already stops the spinners
> >
> > Not really, the new writer will spin in this case, afaics.
> >
> > But this is another problem and probably we do not care. The new writer is
> > almost impossible in this particular case, another freeze_super() should
> > notice frozen != SB_UNFROZEN and return EBUSY.
>
> rwsem_spin_on_owner() checks rwsem_owner_is_writer(), which does owner
> && owner != RWSEM_READER_OWNED, which will fail for !owner.

Yep. So rwsem_spin_on_owner() goes to "out:" and returns
!rwsem_owner_is_reader() == T.

IOW, afaics owner == NULL means "spin unconditionally", I guess this is for
the case when the new writer is going to do rwsem_set_owner() or up_write()
has already called rwsem_clear_owner() but didn't do up_write() yet.

Probably makes sense, but the code is not very clean,

> Or am I completely confused again?

Or me, I am not sure.

Oleg.

Powered by blists - more mailing lists

Powered by Openwall GNU/*/Linux Powered by OpenVZ