From: Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
Subject: Re: Issues with a rather unusual configured NFS server
Date: Mon, 12 Aug 2013 16:36:40 +0200
Message-ID: <20130812143640.GF4596@quack.suse.cz>
References: <52075E01.7030506@gmx.de>
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Cc: Linux NFS mailing list <linux-nfs-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"user-mode-linux-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org"
	<user-mode-linux-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>,
	linux-ext4-u79uwXL29TY76Z2rM5mHXA@public.gmane.org,
	Linux Kernel <linux-kernel-u79uwXL29TY76Z2rM5mHXA@public.gmane.org>,
	"J. Bruce Fields" <bfields-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
To: Toralf =?iso-8859-1?Q?F=F6rster?= <toralf.foerster-Mmb7MZpHnFY@public.gmane.org>
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On Sun 11-08-13 11:48:49, Toralf F=F6rster wrote:
> so that the server either crashes (if it is a user mode linux image) =
or at least its reboot functionality got broken
> - if the NFS server is hammered with scary NFS calls using a fuzzy to=
ol running at a remote NFS client under a non-privileged user id.
>=20
> It can re reproduced, if
> 	- the NFS share is an EXT3 or EXT4 directory
> 	- and it is created at file located at tempfs and mounted via loop d=
evice
> 	- and the NFS server is forced to umount the NFS share
> 	- and the server forced to restart the NSF service afterwards
> 	- and trinity is used
>=20
> I could find a scenario for an automated bisect. 2 times it brought t=
his commit=20
> commit 68a3396178e6688ad7367202cdf0af8ed03c8727
> Author: J. Bruce Fields <bfields-H+wXaHxf7aLQT0dZR+AlfA@public.gmane.org>
> Date:   Thu Mar 21 11:21:50 2013 -0400
>=20
>     nfsd4: shut down more of delegation earlier
  Added Bruce to CC.

> to be the one after which the user mode linux server crashes with a b=
ack trace like this:
>=20
>=20
> $ cat /mnt/ramdisk/bt.v3.11-rc4-172-g8ae3f1d
> [New LWP 14025]
> Core was generated by `/home/tfoerste/devel/linux/linux earlyprintk u=
bda=3D/home/tfoerste/virtual/uml/tr'.
> Program terminated with signal 6, Aborted.
> #0  0xb77ef424 in __kernel_vsyscall ()
> #0  0xb77ef424 in __kernel_vsyscall ()
> #1  0x083a33c5 in kill ()
> #2  0x0807163d in uml_abort () at arch/um/os-Linux/util.c:93
> #3  0x08071925 in os_dump_core () at arch/um/os-Linux/util.c:138
> #4  0x080613a7 in panic_exit (self=3D0x85a1518 <panic_exit_notifier>,=
 unused1=3D0, unused2=3D0x85d6ce0 <buf.15904>) at arch/um/kernel/um_arc=
h.c:240
> #5  0x0809a3b8 in notifier_call_chain (nl=3D0x0, val=3D0, v=3D0x85d6c=
e0 <buf.15904>, nr_to_call=3D-2, nr_calls=3D0x0) at kernel/notifier.c:9=
3
> #6  0x0809a503 in __atomic_notifier_call_chain (nr_calls=3D<optimized=
 out>, nr_to_call=3D<optimized out>, v=3D<optimized out>, val=3D<optimi=
zed out>, nh=3D<optimized out>) at kernel/notifier.c:182
> #7  atomic_notifier_call_chain (nh=3D0x85d6cc4 <panic_notifier_list>,=
 val=3D0, v=3D0x85d6ce0 <buf.15904>) at kernel/notifier.c:191
> #8  0x08400ba8 in panic (fmt=3D0x0) at kernel/panic.c:128
> #9  0x0818edf4 in ext4_put_super (sb=3D0x4a042690) at fs/ext4/super.c=
:818
> #10 0x081010d2 in generic_shutdown_super (sb=3D0x4a042690) at fs/supe=
r.c:418
> #11 0x0810209a in kill_block_super (sb=3D0x0) at fs/super.c:1028
> #12 0x08100f6a in deactivate_locked_super (s=3D0x4a042690) at fs/supe=
r.c:299
> #13 0x08101001 in deactivate_super (s=3D0x4a042690) at fs/super.c:324
> #14 0x08118e0c in mntfree (mnt=3D<optimized out>) at fs/namespace.c:8=
91
> #15 mntput_no_expire (mnt=3D0x0) at fs/namespace.c:929
> #16 0x0811a2f5 in SYSC_umount (flags=3D<optimized out>, name=3D<optim=
ized out>) at fs/namespace.c:1335
> #17 SyS_umount (name=3D134541632, flags=3D0) at fs/namespace.c:1305
> #18 0x0811a369 in SYSC_oldumount (name=3D<optimized out>) at fs/names=
pace.c:1347
> #19 SyS_oldumount (name=3D134541632) at fs/namespace.c:1345
> #20 0x080618e2 in handle_syscall (r=3D0x49e919d4) at arch/um/kernel/s=
kas/syscall.c:35
> #21 0x08073c0d in handle_trap (local_using_sysemu=3D<optimized out>, =
regs=3D<optimized out>, pid=3D<optimized out>) at arch/um/os-Linux/skas=
/process.c:198
> #22 userspace (regs=3D0x49e919d4) at arch/um/os-Linux/skas/process.c:=
431
> #23 0x0805e65c in fork_handler () at arch/um/kernel/process.c:160
> #24 0x00000000 in ?? ()
>=20
>=20
>=20
> A real system however would not crash bug would give a kernel BUG as =
reported here:
> http://article.gmane.org/gmane.comp.file-systems.ext4/38915
  We have deleted inodes (regular files) in the orphan list during
ext4_put_super(). My guess is that NFS is still holding some inode
references to these inodes and thus inodes don't get deleted. So ext3/4
would be just a victim here.

> Furthermore the server won't be able any longer to reboot - it would =
hang
> infinitely in the reboot phase.  Just the magic sysrq keys still work=
s
> then.
  Well, this is likely because the filesystem cannot be shut down.

								Honza
--=20
Jan Kara <jack-AlSwsSmVLrQ@public.gmane.org>
SUSE Labs, CR
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