linux-kernel - Re: [PATCH] iov_iter: don't require contiguous pages in iov_iter_extract_bvec

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Message-ID: <ZyLNqtmxsEt-VYIE@fedora>
Date: Thu, 31 Oct 2024 08:22:02 +0800
From: Ming Lei <ming.lei@...hat.com>
To: Klara Modin <klarasmodin@...il.com>
Cc: Christoph Hellwig <hch@....de>, axboe@...nel.dk,
	akpm@...ux-foundation.org, viro@...iv.linux.org.uk,
	dhowells@...hat.com, linux-block@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
	klara@...m.eu
Subject: Re: [PATCH] iov_iter: don't require contiguous pages in
 iov_iter_extract_bvec_pages

On Thu, Oct 31, 2024 at 08:14:49AM +0800, Ming Lei wrote:
> On Wed, Oct 30, 2024 at 06:56:48PM +0100, Klara Modin wrote:
> > Hi,
> > 
> > On 2024-10-24 07:00, Christoph Hellwig wrote:
> > > From: Ming Lei <ming.lei@...hat.com>
> > > 
> > > The iov_iter_extract_pages interface allows to return physically
> > > discontiguous pages, as long as all but the first and last page
> > > in the array are page aligned and page size.  Rewrite
> > > iov_iter_extract_bvec_pages to take advantage of that instead of only
> > > returning ranges of physically contiguous pages.
> > > 
> > > Signed-off-by: Ming Lei <ming.lei@...hat.com>
> > > [hch: minor cleanups, new commit log]
> > > Signed-off-by: Christoph Hellwig <hch@....de>
> > 
> > With this patch (e4e535bff2bc82bb49a633775f9834beeaa527db in next-20241030),
> > I'm unable to connect via nvme-tcp with this in the log:
> > 
> > nvme nvme1: failed to send request -5
> > nvme nvme1: Connect command failed: host path error
> > nvme nvme1: failed to connect queue: 0 ret=880
> > 
> > With the patch reverted it works as expected:
> > 
> > nvme nvme1: creating 24 I/O queues.
> > nvme nvme1: mapped 24/0/0 default/read/poll queues.
> > nvme nvme1: new ctrl: NQN
> > "nqn.2018-06.eu.kasm.int:freenas:backup:parmesan.int.kasm.eu", addr
> > [2001:0678:0a5c:1204:6245:cbff:fe9c:4f59]:4420, hostnqn:
> > nqn.2018-06.eu.kasm.int:parmesan
> 
> I can't reproduce it by running blktest 'nvme_trtype=tcp ./check nvme/'
> on both next tree & for-6.13/block.
> 
> Can you collect the following bpftrace log by running the script before
> connecting to nvme-tcp?

And please try the following patch:

diff --git a/lib/iov_iter.c b/lib/iov_iter.c
index 9fc06f5fb748..c761f6db3cb4 100644
--- a/lib/iov_iter.c
+++ b/lib/iov_iter.c
@@ -1699,6 +1699,7 @@ static ssize_t iov_iter_extract_bvec_pages(struct iov_iter *i,
                i->bvec++;
                skip = 0;
        }
+       bi.bi_idx = 0;
        bi.bi_size = maxsize + skip;
        bi.bi_bvec_done = skip;



Thanks, 
Ming