Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1753001AbcDORLY (ORCPT ); Fri, 15 Apr 2016 13:11:24 -0400 Received: from mx1.redhat.com ([209.132.183.28]:56078 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752847AbcDORLU convert rfc822-to-8bit (ORCPT ); Fri, 15 Apr 2016 13:11:20 -0400 From: Jeff Moyer To: "Verma\, Vishal L" Cc: "Wilcox\, Matthew R" , "linux-kernel\@vger.kernel.org" , "linux-block\@vger.kernel.org" , "hch\@infradead.org" , "linux-nvdimm\@ml01.01.org" , "xfs\@oss.sgi.com" , "linux-mm\@kvack.org" , "viro\@zeniv.linux.org.uk" , "akpm\@linux-foundation.org" , "axboe\@fb.com" , "linux-fsdevel\@vger.kernel.org" , "linux-ext4\@vger.kernel.org" , "david\@fromorbit.com" , "jack\@suse.cz" Subject: Re: [PATCH v2 5/5] dax: handle media errors in dax_do_io References: <1459303190-20072-1-git-send-email-vishal.l.verma@intel.com> <1459303190-20072-6-git-send-email-vishal.l.verma@intel.com> <1460739288.3012.3.camel@intel.com> X-PGP-KeyID: 1F78E1B4 X-PGP-CertKey: F6FE 280D 8293 F72C 65FD 5A58 1FF8 A7CA 1F78 E1B4 X-PCLoadLetter: What the f**k does that mean? Date: Fri, 15 Apr 2016 13:11:17 -0400 In-Reply-To: <1460739288.3012.3.camel@intel.com> (Vishal L. Verma's message of "Fri, 15 Apr 2016 16:54:48 +0000") Message-ID: User-Agent: Gnus/5.13 (Gnus v5.13) Emacs/24.3 (gnu/linux) MIME-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8BIT Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2237 Lines: 64 "Verma, Vishal L" writes: > On Fri, 2016-04-15 at 12:11 -0400, Jeff Moyer wrote: >> Vishal Verma writes: >> > + if (IS_DAX(inode)) { >> > + ret = dax_do_io(iocb, inode, iter, offset, >> > blkdev_get_block, >> >   NULL, DIO_SKIP_DIO_COUNT); >> > - return __blockdev_direct_IO(iocb, inode, I_BDEV(inode), >> > iter, offset, >> > + if (ret == -EIO && (iov_iter_rw(iter) == WRITE)) >> > + ret_saved = ret; >> > + else >> > + return ret; >> > + } >> > + >> > + ret = __blockdev_direct_IO(iocb, inode, I_BDEV(inode), >> > iter, offset, >> >       blkdev_get_block, NULL, NULL, >> >       DIO_SKIP_DIO_COUNT); >> > + if (ret < 0 && ret_saved) >> > + return ret_saved; >> > + >> Hmm, did you just break async DIO?  I think you did!  :) >> __blockdev_direct_IO can return -EIOCBQUEUED, and you've now turned >> that >> into -EIO.  Really, I don't see a reason to save that first >> -EIO.  The >> same applies to all instances in this patch. > > The reason I saved it was if __blockdev_direct_IO fails for some > reason, we should return the original cause o the error, which was an > EIO.. i.e. we shouldn't be hiding the EIO if the direct_IO fails with > something else.. OK. > But, how does _EIOCBQUEUED work? Maybe we need an exception for it? For async direct I/O, only the setup phase of the I/O is performed and then we return to the caller. -EIOCBQUEUED signifies this. You're heading towards code that looks like this: if (IS_DAX(inode)) { ret = dax_do_io(iocb, inode, iter, offset, blkdev_get_block, NULL, DIO_SKIP_DIO_COUNT); if (ret == -EIO && (iov_iter_rw(iter) == WRITE)) ret_saved = ret; else return ret; } ret = __blockdev_direct_IO(iocb, inode, I_BDEV(inode), iter, offset, blkdev_get_block, NULL, NULL, DIO_SKIP_DIO_COUNT); if (ret < 0 && ret != -EIOCBQUEUED && ret_saved) return ret_saved; There's a lot of special casing here, so you might consider adding comments. Cheers, Jeff