Re: Issues with a rather unusual configured NFS server

["J. Bruce Fields" <bfields@fieldses.org>]

On Mon, Aug 12, 2013 at 04:36:40PM +0200, Jan Kara wrote:
> 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@redhat.com>
> > Date:   Thu Mar 21 11:21:50 2013 -0400
> > 
> >     nfsd4: shut down more of delegation earlier

Thanks for the report.  I think I see the problem--after this commit
nfs4_set_delegation() failures result in nfs4_put_delegation being
called, but nfs4_put_delegation doesn't free the nfs4_file that has
already been set by alloc_init_deleg().

Let me think about how to fix that....

--b.

>   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:
> > 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 works
> > then.
>   Well, this is likely because the filesystem cannot be shut down.
> 
> 								Honza
> -- 
> Jan Kara <jack@suse.cz>
> SUSE Labs, CR
> --
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