Date: Mon, 3 Jun 2024 15:49:09 +0300
From: Ofir Gal <ofir.gal@...umez.com>
To: Hannes Reinecke <hare@...e.de>, 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 03/06/2024 10:24, Hannes Reinecke wrote:
> 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?
Yes, will do.

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