Date: Fri, 16 Jan 2009 16:36:03 +0100
From: Pavel Machek <pavel@suse.cz>
To: Paul Clements <paul.clements@steeleye.com>
Cc: kernel list <linux-kernel@vger.kernel.org>, Andrew Morton <akpm@osdl.org>
Subject: Re: nbd: add locking to nbd_ioctl
Message-ID: <20090116153603.GD2022@elf.ucw.cz>
References: <20090116115512.GA10771@elf.ucw.cz> <4970A696.9070307@steeleye.com>
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On Fri 2009-01-16 10:24:06, Paul Clements wrote:
> Pavel Machek wrote:
>> The code was written with "oh big kernel lock, please protect me from
>> all the evil" mentality: it does not locks its own data structures, it
>> just hopes that big kernel lock somehow helps.
>>
>> It does not. (My fault).
>>
>> So this uses tx_lock to protect data structures from concurrent use
>> between ioctl and worker threads.
>
> What is the particular problem that this fixes? I thought we had already  
> been careful to take tx_lock where necessary to protect data structures.  
>   Perhaps there is something I missed?

for example lo->sock / lo->file are written to without holding any
lock in current code. (lo->xmit_timeout has similar problem, and other
fields, too).

I used tx_lock to protect those fields.
									Pavel
-- 
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