From mboxrd@z Thu Jan  1 00:00:00 1970
From: "hch@infradead.org" <hch@infradead.org>
Subject: Re: [PATCH] hfsplus: fix cross-page bio requests
Date: Tue, 9 Jun 2015 22:05:08 -0700
Message-ID: <20150610050508.GB11894@infradead.org>
References: <1428656543-6790-1-git-send-email-saproj@gmail.com>
 <03D2C0C2-2A16-4018-B24C-28D9011C4446@tuxera.com>
 <CABikg9wzw8eisscJAK1sHV2sJOhPcmq9dsTJcsFreRjbkyJBvw@mail.gmail.com>
Mime-Version: 1.0
Content-Type: text/plain; charset=us-ascii
Cc: Anton Altaparmakov <anton@tuxera.com>,
	"linux-fsdevel@vger.kernel.org" <linux-fsdevel@vger.kernel.org>,
	Anton Altaparmakov <aia21@cam.ac.uk>,
	Al Viro <viro@zeniv.linux.org.uk>,
	"hch@infradead.org" <hch@infradead.org>,
	Andrew Morton <akpm@linux-foundation.org>,
	Vyacheslav Dubeyko <slava@dubeyko.com>,
	Hin-Tak Leung <htl10@users.sourceforge.net>,
	Sougata Santra <sougata@tuxera.com>
To: Sergei Antonov <saproj@gmail.com>
Return-path: <linux-fsdevel-owner@vger.kernel.org>
Received: from bombadil.infradead.org ([198.137.202.9]:60979 "EHLO
	bombadil.infradead.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org
	with ESMTP id S1750784AbbFJFFM (ORCPT
	<rfc822;linux-fsdevel@vger.kernel.org>);
	Wed, 10 Jun 2015 01:05:12 -0400
Content-Disposition: inline
In-Reply-To: <CABikg9wzw8eisscJAK1sHV2sJOhPcmq9dsTJcsFreRjbkyJBvw@mail.gmail.com>
Sender: linux-fsdevel-owner@vger.kernel.org
List-ID: <linux-fsdevel.vger.kernel.org>

On Wed, Jun 10, 2015 at 01:53:47AM +0200, Sergei Antonov wrote:
> >> +     bio = bio_alloc(GFP_NOIO, 1);
> >> +     if (!bio)
> >> +             return -ENOMEM;
> >> +     bio->bi_iter.bi_sector = sector;
> >> +     bio->bi_bdev = sb->s_bdev;
> >> +     bio->bi_vcnt = 1;
> >> +     bio->bi_iter.bi_size = io_size;
> >> +     bio->bi_io_vec[0].bv_page = virt_to_page(buf);
> >> +     bio->bi_io_vec[0].bv_offset = offset_in_page(buf);
> >> +     bio->bi_io_vec[0].bv_len = io_size;
> >>       ret = submit_bio_wait(rw, bio);
> >
> > I think you need to rethink this.  Think of what you are doing: You are adding a single page to the bio but then submitting io that exceeds the page...
> 
> I'm not adding a single page, I'm adding a single vector.
> This "bio->bi_vcnt = 1; bio->bi_io_vec[0].bv_page = ...; etc."
> approach can be found in a number of places in the kernel. Just
> followed other people's example. And I tested the code too :).

And we're getting right of it because it's problematic.  Please allocate
an optimistic numbero of vectors in bio_alloc and use
bio_add_page as only that takes care of the block driver limits
properly.