Date: Wed, 17 Oct 2007 11:18:36 -0700 (PDT)
From: Linus Torvalds <torvalds@linux-foundation.org>
To: Jens Axboe <jens.axboe@oracle.com>
cc: Ingo Molnar <mingo@elte.hu>, linux-kernel@vger.kernel.org,
       Andrew Morton <akpm@linux-foundation.org>
Subject: Re: [bug] block subsystem related crash with latest -git
In-Reply-To: <20071017180042.GP15552@kernel.dk>
Message-ID: <alpine.LFD.0.999.0710171114320.26902@woody.linux-foundation.org>
References: <20071017154655.GA13394@elte.hu>
 <alpine.LFD.0.999.0710170929270.26902@woody.linux-foundation.org>
 <20071017165949.GF15552@kernel.dk> <20071017170804.GG15552@kernel.dk>
 <alpine.LFD.0.999.0710171022340.26902@woody.linux-foundation.org>
 <20071017180042.GP15552@kernel.dk>
MIME-Version: 1.0
Content-Type: TEXT/PLAIN; charset=us-ascii
Sender: linux-kernel-owner@vger.kernel.org
Content-Length: 941
Lines: 25


On Wed, 17 Oct 2007, Jens Axboe wrote:
> > 
> > So avoiding the "sg_next()" on the last entry is pointless. 
> 
> Yeah, I didn't quite understand why if sg was valid, why dereferencing
> *(sg + 1)->page would crap out :/

Actually, I take that back. If 'sg' is the last entry in a *non*linked 
scatter-gather list (ie we don't use the last entry as a link, we actually 
use it as a real SG entry), then "sg_next(sg)" will indeed access past the 
end of the whole allocated array, and will access one past the end.

And with page-alloc debugging, that *will* blow up.

So I think your change to use "sg_next()" only when you actually need a 
next pointer is the correct one after all.

				Linus
-
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/