Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1756128Ab2HWWrK (ORCPT ); Thu, 23 Aug 2012 18:47:10 -0400 Received: from mail-iy0-f174.google.com ([209.85.210.174]:36653 "EHLO mail-iy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752963Ab2HWWrF (ORCPT ); Thu, 23 Aug 2012 18:47:05 -0400 Date: Thu, 23 Aug 2012 15:46:19 -0700 (PDT) From: Hugh Dickins X-X-Sender: hugh@eggly.anvils To: Jeff Moyer cc: "Richard W.M. Jones" , Andrew Morton , Linus Torvalds , Jens Axboe , Torsten Hilbrich , Josh Boyer , linux-kernel@vger.kernel.org Subject: Re: [PATCH] block: replace __getblk_slow misfix by grow_dev_page fix In-Reply-To: Message-ID: References: <20120822115243.GU1448@rhmail.home.annexia.org> User-Agent: Alpine 2.00 (LSU 1167 2008-08-23) MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2748 Lines: 59 On Thu, 23 Aug 2012, Jeff Moyer wrote: > Hugh Dickins writes: > > > [PATCH] block: replace __getblk_slow misfix by grow_dev_page fix > > > > Commit 91f68c89d8f3 ("block: fix infinite loop in __getblk_slow") > > is not good: a successful call to grow_buffers() cannot guarantee > > that the page won't be reclaimed before the immediate next call to > > __find_get_block(), which is why there was always a loop there. > [snip] > > Revert 91f68c89d8f3, restoring __getblk_slow() to how it was (plus > > a checkpatch nitfix). Simplify the interface between grow_buffers() > > and grow_dev_page(), and avoid the infinite loop beyond end of device > > by instead checking init_page_buffers()'s end_block there (I presume > > that's more efficient than a repeated call to blkdev_max_block()), > > returning -ENXIO to __getblk_slow() in that case. > > > > And remove akpm's ten-year-old "__getblk() cannot fail ... weird" > > comment, but that is worrying: are all users of __getblk() really > > now prepared for a NULL bh beyond end of device, or will some oops?? > > Hi, Hugh, > > Thanks for digging into this. I had wondered whether that loop was > required for other purposes, and you've verified that it was. I mostly > like your fix. Returning end_block from init_page_buffers is a little > strange, It is a little strange, I agree. I wrestled a lot with the way block and end_block were known at opposite ends of the callstack, and needed to be brought together for the check. If you think it would be better to move the blkdev_max_block() lookup up a level into grow_dev_page(), then pass end_block down to init_page_buffers(), that could work as well; though we'd then still need to report "failure" from init_page_buffers(). I was inclined to leave it precisely where you had sited it, with that comment on passing it back up; but could change it around if preferred. > but I understand not wanting to redo the call to blkdev_max_block. > > I went ahead to re-tested with the reproducer that I had, and your patch > works fine. Thanks again for tracking this down, and sorry I wasn't > more diligent to begin with. > > Reviewed-and-Tested-by: Jeff Moyer Great, thanks a lot. It (but equally its incorrect earlier version) have been running fine at home under my swapping load. I'm confident that it fixes the issues I had been seeing, although, strictly speaking, it'll take another two or three days to reach bisection confidence level. Hugh -- 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/