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x-vs=clean score=-100 state=0 X-ME-VSCategory: clean X-CM-Envelope: MS4wfJR01bSrdjMBdNKvF1y0mfDwu8wkLMx6ex8Ql/a7c+d5UvvDYIAVMZyvWnIL22dymqkEkJREU4t2dNLeHb+ejsWFZzQexGIrs7Yvi38tPaQ2xmvM9mA5 2i86f+tXaI/3lYvMh33wh6lwzROvwdHLufYzUVNzmOtac3tUJWbFqUy4gaf/m/sJcsSHBCX14kgstYV94e8PptXa18HZVPrF9MBpL0SRHmaweWzREQcai8yY X-CM-Analysis: v=2.3 cv=WaUilXpX c=1 sm=1 tr=0 a=UK1r566ZdBxH71SXbqIOeA==:117 a=UK1r566ZdBxH71SXbqIOeA==:17 a=kj9zAlcOel0A:10 a=VUJBJC2UJ8kA:10 a=VwQbUJbxAAAA:8 a=47cuo1_IehaNXlfTa_IA:9 a=CjuIK1q_8ugA:10 a=x8gzFH9gYPwA:10 a=AjGcO6oz07-iQ99wixmX:22 X-ME-CMScore: 0 X-ME-CMCategory: none Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753512AbeEWAtH (ORCPT ); Tue, 22 May 2018 20:49:07 -0400 Received: from zeniv.linux.org.uk ([195.92.253.2]:52978 "EHLO ZenIV.linux.org.uk" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752654AbeEWAtG (ORCPT ); Tue, 22 May 2018 20:49:06 -0400 Date: Wed, 23 May 2018 01:49:04 +0100 From: Al Viro To: Christoph Hellwig Cc: Avi Kivity , linux-aio@kvack.org, linux-fsdevel@vger.kernel.org, netdev@vger.kernel.org, linux-api@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 08/31] aio: implement IOCB_CMD_POLL Message-ID: <20180523004904.GH30522@ZenIV.linux.org.uk> References: <20180522113108.25713-1-hch@lst.de> <20180522113108.25713-9-hch@lst.de> <20180522220524.GE30522@ZenIV.linux.org.uk> <20180523004530.GG30522@ZenIV.linux.org.uk> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20180523004530.GG30522@ZenIV.linux.org.uk> User-Agent: Mutt/1.9.1 (2017-09-22) Sender: linux-api-owner@vger.kernel.org X-Mailing-List: linux-api@vger.kernel.org X-getmail-retrieved-from-mailbox: INBOX X-Mailing-List: linux-kernel@vger.kernel.org List-ID: On Wed, May 23, 2018 at 01:45:30AM +0100, Al Viro wrote: > Oh, bugger... > > wakeup > removed from queue > schedule __aio_poll_complete() > > cancel > grab ctx->lock > remove from list > work > aio_complete() > check if it's in the list > it isn't, move on to free the sucker > cancel > call ->ki_cancel() > BOOM > > Looks like we want to call ->ki_cancel() *BEFORE* removing from the list, > as well as doing fput() after aio_complete(). The same ordering, BTW, goes > for aio_read() et.al. > > Look: > CPU1: io_cancel() grabs ->ctx_lock, finds iocb and removes it from the list. > CPU2: aio_rw_complete() on that iocb. Since the sucker is not in the list > anymore, we do NOT spin on ->ctx_lock and proceed to free iocb > CPU1: pass freed iocb to ->ki_cancel(). BOOM. BTW, it seems that the mainline is vulnerable to this one. I might be missing something, but...