Date: Mon, 3 Jun 2024 09:24:21 +0200
From: Hannes Reinecke <hare@...e.de>
To: Ofir Gal <ofir.gal@...umez.com>, davem@...emloft.net,
 linux-block@...r.kernel.org, linux-nvme@...ts.infradead.org,
 netdev@...r.kernel.org, ceph-devel@...r.kernel.org
Cc: dhowells@...hat.com, edumazet@...gle.com, pabeni@...hat.com,
 kbusch@...nel.org, axboe@...nel.dk, hch@....de, sagi@...mberg.me,
 philipp.reisner@...bit.com, lars.ellenberg@...bit.com,
 christoph.boehmwalder@...bit.com, idryomov@...il.com, xiubli@...hat.com
Subject: Re: [PATCH v2 0/4] bugfix: Introduce sendpages_ok() to check
 sendpage_ok() on contiguous pages

On 5/30/24 16:24, Ofir Gal wrote:
> skb_splice_from_iter() warns on !sendpage_ok() which results in nvme-tcp
> data transfer failure. This warning leads to hanging IO.
> 
> nvme-tcp using sendpage_ok() to check the first page of an iterator in
> order to disable MSG_SPLICE_PAGES. The iterator can represent a list of
> contiguous pages.
> 
> When MSG_SPLICE_PAGES is enabled skb_splice_from_iter() is being used,
> it requires all pages in the iterator to be sendable.
> skb_splice_from_iter() checks each page with sendpage_ok().
> 
> nvme_tcp_try_send_data() might allow MSG_SPLICE_PAGES when the first
> page is sendable, but the next one are not. skb_splice_from_iter() will
> attempt to send all the pages in the iterator. When reaching an
> unsendable page the IO will hang.
> 
> The patch introduces a helper sendpages_ok(), it returns true if all the
> continuous pages are sendable.
> 
> Drivers who want to send contiguous pages with MSG_SPLICE_PAGES may use
> this helper to check whether the page list is OK. If the helper does not
> return true, the driver should remove MSG_SPLICE_PAGES flag.
> 
> 
> The bug is reproducible, in order to reproduce we need nvme-over-tcp
> controllers with optimal IO size bigger than PAGE_SIZE. Creating a raid
> with bitmap over those devices reproduces the bug.
> 
> In order to simulate large optimal IO size you can use dm-stripe with a
> single device.
> Script to reproduce the issue on top of brd devices using dm-stripe is
> attached below.
> 
> 
> I have added 3 prints to test my theory. One in nvme_tcp_try_send_data()
> and two others in skb_splice_from_iter() the first before sendpage_ok()
> and the second on !sendpage_ok(), after the warning.
> ...
> nvme_tcp: sendpage_ok, page: 0x654eccd7 (pfn: 120755), len: 262144, offset: 0
> skbuff: before sendpage_ok - i: 0. page: 0x654eccd7 (pfn: 120755)
> skbuff: before sendpage_ok - i: 1. page: 0x1666a4da (pfn: 120756)
> skbuff: before sendpage_ok - i: 2. page: 0x54f9f140 (pfn: 120757)
> WARNING: at net/core/skbuff.c:6848 skb_splice_from_iter+0x142/0x450
> skbuff: !sendpage_ok - page: 0x54f9f140 (pfn: 120757). is_slab: 1, page_count: 1
> ...
> 
> 
> stack trace:
> ...
> WARNING: at net/core/skbuff.c:6848 skb_splice_from_iter+0x141/0x450
> Workqueue: nvme_tcp_wq nvme_tcp_io_work
> Call Trace:
>   ? show_regs+0x6a/0x80
>   ? skb_splice_from_iter+0x141/0x450
>   ? __warn+0x8d/0x130
>   ? skb_splice_from_iter+0x141/0x450
>   ? report_bug+0x18c/0x1a0
>   ? handle_bug+0x40/0x70
>   ? exc_invalid_op+0x19/0x70
>   ? asm_exc_invalid_op+0x1b/0x20
>   ? skb_splice_from_iter+0x141/0x450
>   tcp_sendmsg_locked+0x39e/0xee0
>   ? _prb_read_valid+0x216/0x290
>   tcp_sendmsg+0x2d/0x50
>   inet_sendmsg+0x43/0x80
>   sock_sendmsg+0x102/0x130
>   ? vprintk_default+0x1d/0x30
>   ? vprintk+0x3c/0x70
>   ? _printk+0x58/0x80
>   nvme_tcp_try_send_data+0x17d/0x530
>   nvme_tcp_try_send+0x1b7/0x300
>   nvme_tcp_io_work+0x3c/0xc0
>   process_one_work+0x22e/0x420
>   worker_thread+0x50/0x3f0
>   ? __pfx_worker_thread+0x10/0x10
>   kthread+0xd6/0x100
>   ? __pfx_kthread+0x10/0x10
>   ret_from_fork+0x3c/0x60
>   ? __pfx_kthread+0x10/0x10
>   ret_from_fork_asm+0x1b/0x30
> ...
> 
> ---
> Changelog:
> v2, fix typo in patch subject
> 
> Ofir Gal (4):
>    net: introduce helper sendpages_ok()
>    nvme-tcp: use sendpages_ok() instead of sendpage_ok()
>    drbd: use sendpages_ok() to instead of sendpage_ok()
>    libceph: use sendpages_ok() to instead of sendpage_ok()
> 
>   drivers/block/drbd/drbd_main.c |  2 +-
>   drivers/nvme/host/tcp.c        |  2 +-
>   include/linux/net.h            | 20 ++++++++++++++++++++
>   net/ceph/messenger_v1.c        |  2 +-
>   net/ceph/messenger_v2.c        |  2 +-
>   5 files changed, 24 insertions(+), 4 deletions(-)
> 
>   reproduce.sh | 114 +++++++++++++++++++++++++++++++++++++++++++++++++++
>   1 file changed, 114 insertions(+)
>   create mode 100755 reproduce.sh
> 
> diff --git a/reproduce.sh b/reproduce.sh
> new file mode 100755
> index 000000000..8ae226b18
> --- /dev/null
> +++ b/reproduce.sh
> @@ -0,0 +1,114 @@
> +#!/usr/bin/env sh
> +# SPDX-License-Identifier: MIT
> +
> +set -e
> +
> +load_modules() {
> +    modprobe nvme
> +    modprobe nvme-tcp
> +    modprobe nvmet
> +    modprobe nvmet-tcp
> +}
> +
> +setup_ns() {
> +    local dev=$1
> +    local num=$2
> +    local port=$3
> +    ls $dev > /dev/null
> +
> +    mkdir -p /sys/kernel/config/nvmet/subsystems/$num
> +    cd /sys/kernel/config/nvmet/subsystems/$num
> +    echo 1 > attr_allow_any_host
> +
> +    mkdir -p namespaces/$num
> +    cd namespaces/$num/
> +    echo $dev > device_path
> +    echo 1 > enable
> +
> +    ln -s /sys/kernel/config/nvmet/subsystems/$num \
> +        /sys/kernel/config/nvmet/ports/$port/subsystems/
> +}
> +
> +setup_port() {
> +    local num=$1
> +
> +    mkdir -p /sys/kernel/config/nvmet/ports/$num
> +    cd /sys/kernel/config/nvmet/ports/$num
> +    echo "127.0.0.1" > addr_traddr
> +    echo tcp > addr_trtype
> +    echo 8009 > addr_trsvcid
> +    echo ipv4 > addr_adrfam
> +}
> +
> +setup_big_opt_io() {
> +    local dev=$1
> +    local name=$2
> +
> +    # Change optimal IO size by creating dm stripe
> +    dmsetup create $name --table \
> +        "0 `blockdev --getsz $dev` striped 1 512 $dev 0"
> +}
> +
> +setup_targets() {
> +    # Setup ram devices instead of using real nvme devices
> +    modprobe brd rd_size=1048576 rd_nr=2 # 1GiB
> +
> +    setup_big_opt_io /dev/ram0 ram0_big_opt_io
> +    setup_big_opt_io /dev/ram1 ram1_big_opt_io
> +
> +    setup_port 1
> +    setup_ns /dev/mapper/ram0_big_opt_io 1 1
> +    setup_ns /dev/mapper/ram1_big_opt_io 2 1
> +}
> +
> +setup_initiators() {
> +    nvme connect -t tcp -n 1 -a 127.0.0.1 -s 8009
> +    nvme connect -t tcp -n 2 -a 127.0.0.1 -s 8009
> +}
> +
> +reproduce_warn() {
> +    local devs=$@
> +
> +    # Hangs here
> +    mdadm --create /dev/md/test_md --level=1 --bitmap=internal \
> +        --bitmap-chunk=1024K --assume-clean --run --raid-devices=2 $devs
> +}
> +
> +echo "###################################
> +
> +The script creates 2 nvme initiators in order to reproduce the bug.
> +The script doesn't know which controllers it created, choose the new nvme
> +controllers when asked.
> +
> +###################################
> +
> +Press enter to continue.
> +"
> +
> +read tmp
> +
> +echo "# Creating 2 nvme controllers for the reproduction. current nvme devices:"
> +lsblk -s | grep nvme || true
> +echo "---------------------------------
> +"
> +
> +load_modules
> +setup_targets
> +setup_initiators
> +
> +sleep 0.1 # Wait for the new nvme ctrls to show up
> +
> +echo "# Created 2 nvme devices. nvme devices list:"
> +
> +lsblk -s | grep nvme
> +echo "---------------------------------
> +"
> +
> +echo "# Insert the new nvme devices as separated lines. both should be with size of 1G"
> +read dev1
> +read dev2
> +
> +ls /dev/$dev1 > /dev/null
> +ls /dev/$dev2 > /dev/null
> +
> +reproduce_warn /dev/$dev1 /dev/$dev2

Can you convert that into a blktest script?

Cheers,

Hannes
-- 
Dr. Hannes Reinecke                  Kernel Storage Architect
hare@...e.de                                +49 911 74053 688
SUSE Software Solutions GmbH, Frankenstr. 146, 90461 Nürnberg
HRB 36809 (AG Nürnberg), GF: I. Totev, A. McDonald, W. Knoblich

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