From mboxrd@z Thu Jan  1 00:00:00 1970
From: Mike Snitzer <snitzer@redhat.com>
Subject: Re: [PATCH 1/4] dm: remove nr_iovecs parameter from
	alloc_tio()
Date: Fri, 3 Oct 2014 16:01:30 -0400
Message-ID: <20141003200129.GA13982@redhat.com>
References: <542E8CF9.6000609@ce.jp.nec.com> <542E8EA4.2010704@ce.jp.nec.com>
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To: Junichi Nomura <j-nomura@ce.jp.nec.com>
Cc: Jens Axboe <axboe@kernel.dk>, device-mapper development <dm-devel@redhat.com>, Kent Overstreet <kmo@daterainc.com>
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On Fri, Oct 03 2014 at  7:55am -0400,
Junichi Nomura <j-nomura@ce.jp.nec.com> wrote:

> alloc_tio() allocates a bio for clone. It takes the number of
> bvecs to allocate for the clone-bio.
> However, with the introduction of bio_clone_fast() in v3.14,
> we no longer need to allocate bvecs and nr_iovecs is always 0.
> 
> __clone_and_map_simple_bio() looks like passing non-zero
> nr_iovecs, but its value is always within the range of
> inline bvecs and no allocation actually happens.
> If allocation happened, BUG_ON() in __bio_clone_fast() would
> trigger.
> 
> This patch removes the nr_iovecs parameter from alloc_tio()
> to prevent possible future mis-use of the interface.
> 
> Signed-off-by: Jun'ichi Nomura <j-nomura@ce.jp.nec.com>

I picked this patch up and staged in linux-dm.git's for-next, see:
https://git.kernel.org/cgit/linux/kernel/git/device-mapper/linux-dm.git/commit/?h=for-next&id=8d59090cdc0ea91ffc390f78d0406baf8f66ae38