From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from ivanoab6.miniserver.com ([5.153.251.140] helo=www.kot-begemot.co.uk) by merlin.infradead.org with esmtps (Exim 4.90_1 #2 (Red Hat Linux)) id 1gKLLw-0004P0-Ly for linux-um@lists.infradead.org; Wed, 07 Nov 2018 10:46:29 +0000 Subject: Re: 4.20-rc1 looks broken for UML References: <4a096c4f-6552-dbcb-676b-a87306dde07a@kot-begemot.co.uk> <6298063.A9SzxUBULK@blindfold> <2177266.HJA9EnQ7lp@blindfold> <20181107075318.GA24381@lst.de> From: Anton Ivanov Message-ID: <31d79c23-0fa0-956e-5477-0c326416fc45@kot-begemot.co.uk> Date: Wed, 7 Nov 2018 10:46:05 +0000 MIME-Version: 1.0 In-Reply-To: <20181107075318.GA24381@lst.de> Content-Language: en-US List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Sender: "linux-um" Errors-To: linux-um-bounces+geert=linux-m68k.org@lists.infradead.org To: Christoph Hellwig , Richard Weinberger Cc: axboe@kernel.dk, linux-um@lists.infradead.org On 11/7/18 7:53 AM, Christoph Hellwig wrote: > On Tue, Nov 06, 2018 at 09:49:45PM +0100, Richard Weinberger wrote: >> Christoph, >> >> Anton found a problem in your "ubd: remove use of blk_rq_map_sg" patch. >> With CONFIG_DEBUG_PAGEALLOC enabled, the ubd driver crashes because it tries >> to deref address 0x12345678, which is the poison from store_stackinfo(). >> >> Please see below for more info. >> Can it be that your change introduced a use-after-free bug in UML's block driver? > Sounds like it. But I'll need some more time to debug it. I had to revert 4e6da0fe8058df9bfa937902fcd9cb2b7b89b2df "um: Convert ubd driver to blk-mq" as well to get things back to business as usual. The block-mq driver works for reading - no issues if everything is ro. It also clearly works for writing for some configs in older kernels, otherwise it would have been picked up. Something changed in 4.20-rc1 which made it fail in my config. The failure is instantaneous for 4.20-rc1 with only ecb0a83e3198f2c1142901687afacbc73602a13b " ubd: remove use of blk_rq_map_sg" reverted. Reverting both and restoring the driver to 4.19 state fixes things. I am going to give it a go to debug exactly what breaks for writing in ecb0a83e3198f2c1142901687afacbc73602a13b " ubd: remove use of blk_rq_map_sg". A. > > _______________________________________________ > linux-um mailing list > linux-um@lists.infradead.org > http://lists.infradead.org/mailman/listinfo/linux-um > _______________________________________________ linux-um mailing list linux-um@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-um