Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1758182Ab2EAQPf (ORCPT ); Tue, 1 May 2012 12:15:35 -0400 Received: from mail-gy0-f174.google.com ([209.85.160.174]:37623 "EHLO mail-gy0-f174.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1757694Ab2EAQPd convert rfc822-to-8bit (ORCPT ); Tue, 1 May 2012 12:15:33 -0400 MIME-Version: 1.0 In-Reply-To: <1335778207-6511-1-git-send-email-jack@suse.cz> References: <1335778207-6511-1-git-send-email-jack@suse.cz> From: KOSAKI Motohiro Date: Tue, 1 May 2012 12:15:11 -0400 Message-ID: Subject: Re: [PATCH] Describe race of direct read and fork for unaligned buffers To: Jan Kara Cc: Michael Kerrisk , LKML , linux-man@vger.kernel.org, linux-mm@kvack.org, mgorman@suse.de, Jeff Moyer Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1048 Lines: 31 > +suffices. However, if the user buffer is not page aligned and direct read One more thing. direct write also makes data corruption. Think following scenario, 1) P1-T1 uses DIO write (and starting dma) 2) P1-T2 call fork() and makes P2 3) P1-T3 write to the dio target page. and then, cow break occur and original dio target pages is now owned by P2. 4) P2 write the dio target page. It now does NOT make cow break. and now we break dio target page data. 5) DMA transfer write invalid data to disk. The detail is described in your refer URLs. > +runs in parallel with a > +.BR fork (2) > +of the reader process, it may happen that the read data is split between > +pages owned by the original process and its child. Thus effectively read > +data is corrupted. > ?.LP > ?The > ?.B O_DIRECT -- 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/