linux-kernel - Re: [PATCH] [0/11] SYSCTL: Use RCU to avoid races with string sysctls

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Message-ID: <20091221032104.GB25372@basil.fritz.box>
Date:	Mon, 21 Dec 2009 04:21:04 +0100
From:	Andi Kleen <andi@...stfloor.org>
To:	"Eric W. Biederman" <ebiederm@...ssion.com>
Cc:	Andi Kleen <andi@...stfloor.org>, linux-kernel@...r.kernel.org,
	paulmck@...ux.vnet.ibm.com
Subject: Re: [PATCH] [0/11] SYSCTL: Use RCU to avoid races with string
	sysctls

> So we have sysctl have locking problems, not new sysctl regressions.

Ok.

> > If the strings were made a bit smaller this could be also 
> > put on the stack, but I didn't dare for 256 bytes. 
> 
> Hmm.  rcu wise that sounds wrong, but I haven't looked into your

What sounds wrong? 

The reason for the copies is that when the reader sleeps 
rcu_read_lock() cannot be used to protect the string completely,
so it copies instead.

The alternative would have been to use SRCU, but I didn't like that.

> cool new data structure yet.

It's not really particularly new or cool, it's just a simple RCU wrapper
around a string.

-Andi

-- 
ak@...ux.intel.com -- Speaking for myself only.
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