Date: Thu, 23 Feb 2006 16:16:31 -0800
From: Andrew Morton <akpm@osdl.org>
To: Benjamin LaHaise <bcrl@kvack.org>
Cc: stern@rowland.harvard.edu, sekharan@us.ibm.com,
       linux-kernel@vger.kernel.org
Subject: Re: [PATCH] Avoid calling down_read and down_write during startup
Message-Id: <20060223161631.6f8fa41d.akpm@osdl.org>
In-Reply-To: <20060223223729.GE30329@kvack.org>
References: <20060223110350.49c8b869.akpm@osdl.org>
	<Pine.LNX.4.44L0.0602231728300.4579-100000@iolanthe.rowland.org>
	<20060223223729.GE30329@kvack.org>
Mime-Version: 1.0
Content-Type: text/plain; charset=US-ASCII
Content-Transfer-Encoding: 7bit
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 935
Lines: 19

Benjamin LaHaise <bcrl@kvack.org> wrote:
>
> On Thu, Feb 23, 2006 at 05:36:56PM -0500, Alan Stern wrote:
>  > This patch (as660) changes the registration and unregistration routines 
>  > for blocking notifier chains.  During system startup, when task switching 
>  > is illegal, the routines will avoid calling down_write().
> 
>  Why is that necessary?  The down_write() will immediately succeed as no 
>  other process can possibly be holding the lock when the system is booting, 
>  so the special casing doesn't fix anything.

down_write() unconditionally (and reasonably) does local_irq_enable() in
the uncontended case.  And enabling local interrupts early in boot can
cause crashes.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at  http://vger.kernel.org/majordomo-info.html
Please read the FAQ at  http://www.tux.org/lkml/