[PATCH] iov_iter: don't require contiguous pages in iov_iter_extract_bvec_pages

[Ming Lei]

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 at redhat.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 at redhat.com>
> > [hch: minor cleanups, new commit log]
> > Signed-off-by: Christoph Hellwig <hch at lst.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?

Please enable the following kernel options for bpftrace:

	CONFIG_KPROBE_EVENTS_ON_NOTRACE=y
	CONFIG_NVME_CORE=y
	CONFIG_NVME_FABRICS=y
	CONFIG_NVME_TCP=y

Btw, bpftrace doesn't work on next tree if nvme is built as module.


# cat extract.bt
#!/usr/bin/bpftrace

kprobe:nvmf_connect_io_queue
{
	@connect[tid]=1;
}

kretprobe:nvmf_connect_io_queue
{
	@connect[tid]=0;
}

kprobe:iov_iter_extract_pages
/@connect[tid]/
{
	$i = (struct iov_iter *)arg0;
	printf("extract pages: iter(cnt %lu off %lu) maxsize %u maxpages %u offset %lu\n",
		$i->count, $i->iov_offset, arg2, arg3, *((uint32 *)arg4));
	printf("\t bvec(off %u len %u)\n", $i->bvec->bv_offset, $i->bvec->bv_len);
}

kretprobe:iov_iter_extract_pages
/@connect[tid]/
{
	printf("extract pages: ret %d\n", retval);
}

END {
	clear(@connect);
}



Thanks,
Ming