On Tue, 20 Sep 2011, J. Bruce Fields wrote:
On Fri, Aug 26, 2011 at 10:58:15PM +0200, Jan-Marek Glogowski wrote:
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Hi
I'm on Debian Squeeze using NFSv4 (2.6.32 / 1.1.2). Groups ares
stored in LDAP and one contains a space. If I want to chgrp a file,
the chown system call gets stuck and I get an kernel "hung_task"
backtrace:
[76920.364077] INFO: task chown:31709 blocked for more than 120 seconds.
[76920.364781] "echo 0 > /proc/sys/kernel/hung_task_timeout_secs" disables this message.
[76920.365894] chown D 0000000000000000 0 31709 28415 0x00000004
[76920.365900] ffffffff814611f0 0000000000000086 0000000000000000 ffff88000886de88
[76920.365906] ffff88000886dde8 ffffffff810f6211 000000000000f9e0 ffff88000886dfd8
[76920.365910] 0000000000015780 0000000000015780 ffff88003ed269f0 ffff88003ed26ce8
[76920.365914] Call Trace:
[76920.365927] [<ffffffff810f6211>] ? path_to_nameidata+0x15/0x37
[76920.365933] [<ffffffff811035cd>] ? mntput_no_expire+0x23/0xee
[76920.365940] [<ffffffff812fb99b>] ? __mutex_lock_common+0x122/0x192
[76920.365945] [<ffffffff810f9c1c>] ? user_path_at+0x52/0x79
[76920.365948] [<ffffffff812fbac3>] ? mutex_lock+0x1a/0x31
[76920.365954] [<ffffffff810ed746>] ? chown_common+0x5b/0x7c
[76920.365958] [<ffffffff812fe9f6>] ? do_page_fault+0x2e0/0x2fc
[76920.365962] [<ffffffff810ed982>] ? sys_fchownat+0x53/0x70
[76920.365967] [<ffffffff81010b42>] ? system_call_fastpath+0x16/0x1b
[77240.440046] nfs: server buildserv-next not responding, still trying
[95664.836086] nfs: server buildserv-next not responding, still trying
[96568.599435] nfs: server buildserv-next OK
So I backported the Debian nfs-utils 1.1.4 and updated the kernel to
the squeeze-backports version (2.6.39).
The backtrace is now gone, but the chgrp process is still stuck.
The client rpc.idmapd seems to be fine:
Aug 26 20:41:41 kvm-auth rpc.idmapd[973]: nfs4_gid_to_name: calling nsswitch->gid_to_name
Aug 26 20:41:41 kvm-auth rpc.idmapd[973]: nfs4_gid_to_name: nsswitch->gid_to_name returned 0
Aug 26 20:41:41 kvm-auth rpc.idmapd[973]: nfs4_gid_to_name: final return value is 0
Aug 26 20:41:41 kvm-auth rpc.idmapd[973]: Client 0: (group) id "1094" -> name "Domain Administrators@xxxxxxxxxxxxxxx"
On the server side I see idmapd errors in the daemon.log (every 2
minutes, so I guess the backtrace is just suppressed - same as the
previous 120 sec timeout):
Aug 26 20:27:48 buildserv-next rpc.idmapd[16848]: nfsdcb: authbuf=* authtype=group
Aug 26 20:27:48 buildserv-next rpc.idmapd[16848]: nfsdcb: bad name in upcall
There is an invalid check in the idmapd code, which converts the
octal encoded values back to the original characters (see attached
patch).
The patch makes sense to me, thanks; steved, could you apply?
What I don't know is how to implement the "real" error handling. I
don't think the client process should be stuck forever, just because
the server fails to find the encoded name.
Agreed that if a name couldn't be mapped, we do still want to respond to
the kernel to tell it that, so that it can handle the problem and
continue. I think we do that correctly.
I think this case is a little different--if we have a failure here in
the decoding, it means that there's a bug somewhere, either in the
kernel's encoding or our parsing. In that case there's no real recourse
other than logging an error and hoping a helpful user tells us about it!
I have no knowledge of the NFS protocol or NFS error handling, but from my
POV, I would expect something like a NFS server error telling the client,
that the server can't comply (probably even including the reason "I don't
know your group") - and EIO from the chgrp syscall.
At the end this boils down to:
1. Wait forever until the server recovers or the user aborts manually or
2. Tell the user about the current server problem and abort the request.
And that's were we have the soft and hard mount options - I just forgot,
that the default is hard and then this behaviour is expected :-)
Jan-Marek
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