linux-kernel - Re: [PATCH, RFC] fasync() BKL pushdown

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Message-ID: <485C0133.3020708@firstfloor.org>
Date:	Fri, 20 Jun 2008 21:12:51 +0200
From:	Andi Kleen <andi@...stfloor.org>
To:	Jonathan Corbet <corbet@....net>
CC:	LKML <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	Al Viro <viro@...IV.linux.org.uk>
Subject: Re: [PATCH, RFC] fasync() BKL pushdown

Jonathan Corbet wrote:
> On Fri, 20 Jun 2008 19:55:03 +0200
> Andi Kleen <andi@...stfloor.org> wrote:
> 
>> Jonathan Corbet wrote:
>>
>>> The majority of fasync() functions just call fasync_helper() with a
>>> pointer to an fasync_struct reachable from the file structure.
>>> Given that (1) the struct file will not go away while fasync() is
>>> running, and (2) the VFS-level fasync() stuff is protected with the
>>> Big Fasync Lock, I contend that these simple implementations have
>>> no need for the BKL.  
>> Not necessarily true, they might require BKL still for fd live time
>> issues.
> 
> Could you help me out a bit here?  I'm even slower than usual when it
> comes to VFS stuff.  As far as I can tell, the given file cannot go
> away during the call to fasync(), as sys_fcntl() holds a reference on
> it.  Are you saying that something else can happen during that time?

Some devices do state change even when the reference count is > 0.
Would need to double check it's all ok with the fasync list.

Anyways I did this auditing for the cases where I used unlocked_ioctl
[but I think I wanted to redo it because i wasn't 100% sure anymore]
and I haven't done it at all for the cases that weren't converted.

-Andi

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