Re: Issues with a rather unusual configured NFS server

From: Jan Kara
Date: Mon Aug 12 2013 - 10:36:50 EST

On Sun 11-08-13 11:48:49, Toralf Förster 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 tool running at a remote NFS client under a non-privileged user id.
> 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 device
> - 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
> I could find a scenario for an automated bisect. 2 times it brought this commit
> commit 68a3396178e6688ad7367202cdf0af8ed03c8727
> Author: J. Bruce Fields <bfields@xxxxxxxxxx>
> Date: Thu Mar 21 11:21:50 2013 -0400
> 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 back trace like this:
> $ cat /mnt/ramdisk/bt.v3.11-rc4-172-g8ae3f1d
> [New LWP 14025]
> Core was generated by `/home/tfoerste/devel/linux/linux earlyprintk ubda=/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=0x85a1518 <panic_exit_notifier>, unused1=0, unused2=0x85d6ce0 <buf.15904>) at arch/um/kernel/um_arch.c:240
> #5 0x0809a3b8 in notifier_call_chain (nl=0x0, val=0, v=0x85d6ce0 <buf.15904>, nr_to_call=-2, nr_calls=0x0) at kernel/notifier.c:93
> #6 0x0809a503 in __atomic_notifier_call_chain (nr_calls=<optimized out>, nr_to_call=<optimized out>, v=<optimized out>, val=<optimized out>, nh=<optimized out>) at kernel/notifier.c:182
> #7 atomic_notifier_call_chain (nh=0x85d6cc4 <panic_notifier_list>, val=0, v=0x85d6ce0 <buf.15904>) at kernel/notifier.c:191
> #8 0x08400ba8 in panic (fmt=0x0) at kernel/panic.c:128
> #9 0x0818edf4 in ext4_put_super (sb=0x4a042690) at fs/ext4/super.c:818
> #10 0x081010d2 in generic_shutdown_super (sb=0x4a042690) at fs/super.c:418
> #11 0x0810209a in kill_block_super (sb=0x0) at fs/super.c:1028
> #12 0x08100f6a in deactivate_locked_super (s=0x4a042690) at fs/super.c:299
> #13 0x08101001 in deactivate_super (s=0x4a042690) at fs/super.c:324
> #14 0x08118e0c in mntfree (mnt=<optimized out>) at fs/namespace.c:891
> #15 mntput_no_expire (mnt=0x0) at fs/namespace.c:929
> #16 0x0811a2f5 in SYSC_umount (flags=<optimized out>, name=<optimized out>) at fs/namespace.c:1335
> #17 SyS_umount (name=134541632, flags=0) at fs/namespace.c:1305
> #18 0x0811a369 in SYSC_oldumount (name=<optimized out>) at fs/namespace.c:1347
> #19 SyS_oldumount (name=134541632) at fs/namespace.c:1345
> #20 0x080618e2 in handle_syscall (r=0x49e919d4) at arch/um/kernel/skas/syscall.c:35
> #21 0x08073c0d in handle_trap (local_using_sysemu=<optimized out>, regs=<optimized out>, pid=<optimized out>) at arch/um/os-Linux/skas/process.c:198
> #22 userspace (regs=0x49e919d4) at arch/um/os-Linux/skas/process.c:431
> #23 0x0805e65c in fork_handler () at arch/um/kernel/process.c:160
> #24 0x00000000 in ?? ()
> A real system however would not crash bug would give a kernel BUG as reported here:
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 works
> then.
Well, this is likely because the filesystem cannot be shut down.

Jan Kara <jack@xxxxxxx>
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