Date: Thu, 26 Sep 2013 23:57:58 +0000 (GMT)
From: Jongman Heo <jongman.heo@samsung.com>
Subject: Re: Re: Re: Regression caused by commit 4bdc33ed
 ("NFSDv4.2: Add NFS v4.2 support to the NFS server")
To: "J. Bruce Fields" <bfields@fieldses.org>,
        "linux-nfs@vger.kernel.org" <linux-nfs@vger.kernel.org>,
        "linux-kernel@vger.kernel.org" <linux-kernel@vger.kernel.org>
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Hi,Bruce,

>
>------- Original Message -------
>Sender : J. Bruce Fields<bfields@fieldses.org>
>Date : 2013-09-27 02:47 (GMT+09:00)
>Title : Re: Re: Regression caused by commit 4bdc33ed ("NFSDv4.2: Add NFS v4.2 support to the NFS server")
>
>On Thu, Sep 26, 2013 at 04:22:48AM +0000, Jongman Heo wrote:
>> 
>> Hi,
>> 
>> >
>> >------- Original Message -------
>> >Sender : J. Bruce Fields
>> >Date : 2013-09-25 23:05 (GMT+09:00)
>> >Title : Re: Regression caused by commit 4bdc33ed ("NFSDv4.2: Add NFS v4.2 support to the NFS server")
>> >
>> >On Wed, Sep 25, 2013 at 05:19:50AM +0000, Jongman Heo wrote:
>> >> My embedded development box fails to NFS-boot with NFS server which uses recent kernel.
>> >> 
>> >> Using git bisect, I found it is caused by commit 4bdc33ed ("NFSDv4.2: Add NFS v4.2 support to the NFS server").
>> >> 
>> >> 
>> >> 1. dmesg (NFS boot failure case)
>> >> 
>> >> ...
>> >> [    2.040893] ADDRCONF(NETDEV_UP): eth0: link is not ready
>> >> [    2.046207] e1000: eth0 NIC Link is Up 1000 Mbps Full Duplex, Flow Control: RX
>> >> [    2.053570] ADDRCONF(NETDEV_CHANGE): eth0: link becomes ready
>> >> [    3.055023] IP-Config: Guessing netmask 255.255.0.0
>> >> [    3.059979] IP-Config: Gateway not on directly connected network.
>> >> [    3.066330] Looking up port of RPC 100003/2 on 165.213.88.249
>> >> [    3.074001] Looking up port of RPC 100005/1 on 165.213.88.249
>> >> [    3.122878] VFS: Unable to mount root fs via NFS, trying floppy.
>> >> [    3.129134] VFS: Cannot open root device "nfs" or unknown-block(2,0)
>> >> [    3.135478] Please append a correct "root=" boot option; here are the available partitions:
>> >> [    3.143831] 1f00            3072 mtdblock0 (driver?)
>> >> [    3.148798] 1f01              64 mtdblock1 (driver?)
>> >> [    3.153758] 1f02              64 mtdblock2 (driver?)
>> >> [    3.158719] 1f03              64 mtdblock3 (driver?)
>> >> [    3.163682] 1f04              64 mtdblock4 (driver?)
>> >> [    3.168644] 1f05              64 mtdblock5 (driver?)
>> >> [    3.173607] 1f06              64 mtdblock6 (driver?)
>> >> [    3.178568] 0800       488386584 sda driver: sd
>> >> [    3.183099]   0801          506016 sda1
>> >> [    3.186927]   0802         4008217 sda2
>> >> [    3.190755]   0803       483869767 sda3
>> >> [    3.194584] b300         1880064 mmcblk0 driver: mmcblk
>> >> [    3.199802]   b301            4096 mmcblk0p1
>> >> [    3.204063]   b302          102400 mmcblk0p2
>> >> [    3.208330]   b303            4096 mmcblk0p3
>> >> [    3.212594]   b304               1 mmcblk0p4
>> >> [    3.216855]   b305            2048 mmcblk0p5
>> >> [    3.221116]   b306            2048 mmcblk0p6
>> >> [    3.225382]   b307            2048 mmcblk0p7
>> >> [    3.229644]   b308            4096 mmcblk0p8
>> >> [    3.233906]   b309           12288 mmcblk0p9
>> >> [    3.238176]   b30a           16384 mmcblk0p10
>> >> [    3.242524]   b30b          142336 mmcblk0p11
>> >> [    3.246869]   b30c         1572864 mmcblk0p12
>> >> [    3.251219] b320           12288 mmcblk0gp1 (driver?)
>> >> [    3.256272] b310           12288 mmcblk0gp0 (driver?)
>> >> [    3.261320] Kernel panic - not syncing: VFS: Unable to mount root fs on unknown-block(2,0)
>> >> [    3.269566] Pid: 1, comm: swapper Not tainted 2.6.35 #1
>> >> [    3.274776] Call Trace:
>> >> [    3.277232]  [<80d0db5b>] ? printk+0x1e/0x20
>> >> [    3.281492]  [<80d0dad1>] panic+0x65/0xd1
>> >> [    3.285495]  [<80eb9ce3>] mount_block_root+0x125/0x1be
>> >> [    3.290631]  [<809d1f6d>] ? sys_mknod+0x2d/0x30
>> >> [    3.295156]  [<80eb9f6d>] mount_root+0xd0/0xf2
>> >> [    3.299591]  [<80eba0d9>] prepare_namespace+0x14a/0x184
>> >> [    3.304803]  [<809c44f6>] ? sys_access+0x26/0x30
>> >> [    3.309411]  [<80eb9a4e>] kernel_init+0x25e/0x26e
>> >> [    3.314105]  [<80eb97f0>] ? kernel_init+0x0/0x26e
>> >> [    3.318800]  [<80903242>] kernel_thread_helper+0x6/0x10
>> >> 
>> >> 
>> >> 2. Client (my embedded box) configuration
>> >>   It's kernel 2.6.35 based, and has following NFS kernel configs.
>> >> 
>> >> # grep NFS .config
>> >> CONFIG_NFS_FS=y
>> >> CONFIG_NFS_V3=y
>> >> CONFIG_NFS_V3_ACL=y
>> >> CONFIG_NFS_V4=y
>> >> # CONFIG_NFS_V4_1 is not set
>> >> CONFIG_ROOT_NFS=y
>> >> # CONFIG_NFSD is not set
>> >> CONFIG_NFS_ACL_SUPPORT=y
>> >> CONFIG_NFS_COMMON=y
>> >> 
>> >> 
>> >> 3. Server (NFSD) configuration
>> >>    Fedora 19 + latest linus git kernel 3.12.0-rc2+ (commit 22356f44, mm: Place preemption point in do_mlockall() loop)
>> >> 
>> >> 
>> >> 4. workaround
>> >> 
>> >> Reverting the commit 4bdc33ed resolves my issue, NFS boot is working then.
>> >> I've done git bisect, but lost the resulting bisect log due to sudden power loss :(.
>> >
>> >So when you say you revert that commit, you mean you revert it on your
>> >*server*, right?  You're not changing the client at all throughout these
>> >tests?
>> 
>> Right. I reverted the commit on my server, while client is same throughout the tests.
>> 
>> >
>> >A network trace might be interesting: so, on the server, run
>> >
>> >tcpdump -s0 -wtmp.pcap -ieth0
>> >
>> >(replace eth0 by the right network interface), then try booting the
>> >client and after the client fails, kill tcpdump and send us a copy of
>> >tmp.pcap.
>> >
>> >(And also you might want to fire up "wireshark tmp.pcap" and take a look
>> >yourself--you'll probably see something like a version mismatch error in
>> >the network traffic.)
>> >
>> >--b.
>> 
>> I've attached two tcpdump files. 
>> In the dump, 165.213.88.238 is IP address for NFS client (embedded box with 2.6.35 kernel), and 192.168.64.128 is for NFS server (running latest git kernel with and without the commit revert)
>> 
>>  * tmp_good_filtered.pcap
>>    - latest linus git tree + commit 4bdc33ed reverted
>>    - NFS boot is working
>> 
>>  * tmp_bad_filtered.pcap
>>    - latest linus git tree
>>    - NFS boot doesn't work
>>  
>> In error case, I can see following message from wireshark packet window ;
>> 
>>     Accept State: remote can't support version # (2)
>>     Program Version (Minimum): 3
>>     Program Version (Maximum): 4
>
>This is pretty weird--it's not at all obvious how that patch would
>affect this.
>
>You're absolutely positive that the *only* thing you're changing on the
>server between the "good" and "bad" cases is that one kernel patch?
>You're not changing anything in userspace?
>

Yes, pretty sure.

>What does "cat /proc/fs/nfsd/versions" report in the good and bad cases?
>
>(BTW, out of curiosity: what kind of client is this that only supports
>NFSv2 and NFSv3?  Even for an embedded system that's a bit surprising.)
>
>--b.
>

Here are /proc/fs/nfsd/versions information for good and bad cases ;

good (commit 4bdc33ed reverted)

# cat /proc/fs/nfsd/versions 
+2 +3 +4 +4.1


bad (current linus git)

# cat /proc/fs/nfsd/versions  
-2 +3 +4 +4.1 -4.2


I don't know why the commit 4bdc33ed makes this difference ( from +2 to -2 ).

My NFS server just uses Fedora 19 + latest kernel (which is not a rare setup...), 
so I think some people can verify if this version information change happens w/ and w/o the commit revert.

Don't know the detail of NFS protocol, but our NFS client seems not to try with v3 and v4 in case v2 fails...
Is this an unexpected (buggy) behavior of my old embedded box (NFS client of kernel 2.6.35), or expected one from the NFS protocol?

Thanks,
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