Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S935537AbXJQVNX (ORCPT ); Wed, 17 Oct 2007 17:13:23 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1757655AbXJQVNP (ORCPT ); Wed, 17 Oct 2007 17:13:15 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:52074 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757409AbXJQVNO (ORCPT ); Wed, 17 Oct 2007 17:13:14 -0400 Date: Wed, 17 Oct 2007 14:11:34 -0700 (PDT) From: Linus Torvalds To: Jens Axboe cc: Ingo Molnar , linux-kernel@vger.kernel.org, Jeff Garzik , Alan Cox Subject: Re: [bug] ata subsystem related crash with latest -git In-Reply-To: <20071017203140.GF15552@kernel.dk> Message-ID: References: <20071017174503.GA4622@elte.hu> <20071017175337.GN15552@kernel.dk> <20071017183716.GU15552@kernel.dk> <20071017190901.GA13780@elte.hu> <20071017193542.GA15552@kernel.dk> <20071017195659.GD15552@kernel.dk> <20071017200638.GE15552@kernel.dk> <20071017203140.GF15552@kernel.dk> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=us-ascii Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1970 Lines: 60 On Wed, 17 Oct 2007, Jens Axboe wrote: > > That would hurt... Care to commit your for_each_sg() uglification fixup > for now then? Or disable the allocation debug config entry, so that the > sg+1 deref wont crash? Well, in practice, it will only crash with DEBUG_PAGEALLOC, so few enough are going to be hit by it. In that sense I don't think we're in any deep trouble yet. That said, maybe this is an acceptable, if hacky, replacement for the current "for_each_sg()" loop. It does: - starts at one *before* the sglist - does the sg_next() at the *top* of the loop rather than the bottom of it - has a "--count" before that sg_next, so that we don't do it for the case when we break out and have used up all segments. Totally untested, but it *may* work, and it doesn't look horribly ugly. Ingo, does this actually make any difference? Linus --- include/linux/scatterlist.h | 9 ++++++++- 1 files changed, 8 insertions(+), 1 deletions(-) diff --git a/include/linux/scatterlist.h b/include/linux/scatterlist.h index 2dc7464..f5c8e11 100644 --- a/include/linux/scatterlist.h +++ b/include/linux/scatterlist.h @@ -51,11 +51,18 @@ static inline struct scatterlist *sg_next(struct scatterlist *sg) return sg; } +static inline struct scatterlist *sg_safe_next(struct scatterlist *sg, int left) +{ + if (left < 0) + return NULL; + return sg_next(sg); +} + /* * Loop over each sg element, following the pointer to a new list if necessary */ #define for_each_sg(sglist, sg, nr, __i) \ - for (__i = 0, sg = (sglist); __i < (nr); __i++, sg = sg_next(sg)) + for (__i = (nr), sg = (sglist)-1; (sg = sg_safe_next(sg, --__i)) != NULL ; ) /** * sg_last - return the last scatterlist entry in a list - 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/