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Date: Fri, 9 Jan 2009 15:03:54 +0100
From: Oleg Nesterov <oleg@redhat.com>
To: Jonathan Corbet <corbet@lwn.net>
Cc: LKML <linux-kernel@vger.kernel.org>, Andi Kleen <andi@firstfloor.org>,
       Alan Cox <alan@lxorguk.ukuu.org.uk>, Al Viro <viro@ZenIV.linux.org.uk>,
       bfields@fieldses.org
Subject: Re: RFC: Fix f_flags races without the BKL
Message-ID: <20090109140354.GA6018@redhat.com>
References: <20081229041352.6bbdf57c@tpl> <20081229124151.GA29634@redhat.com> <20090108162806.48caaa29@bike.lwn.net> <20090109100821.GA27829@redhat.com> <20090109061846.5beee8df@bike.lwn.net>
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On 01/09, Jonathan Corbet wrote:
>
> On Fri, 9 Jan 2009 11:08:21 +0100
> Oleg Nesterov <oleg@redhat.com> wrote:
>
> > and then we change f_flags again, including F_ASYNC bit.
> >
> > This is racy?
>
> No, I took FASYNC out of SETFL_MASK, so it isn't changed here.

Ah yes, I missed the change in SETFL_MASK. Thanks.

> > Now we have the global mutex for ->fasync... Well, not very
> > good but fasync_helper() takes fasync_lock anyway.
>
> Not very good, but does anybody know of a workload which would result in
> that mutex being contended ever?

I don't.

Actually, I personally dislike the global file_flags_lock more.
But don't get me wrong, I do not think O_LOCK_FLAGS is better
or cleaner.

Oleg.