Re: 3.17.0+ files disappearing after playing old dos game on nfsroot laptop

[Eric W. Biederman]

Hans de Bruin <jmdebruin@xxxxxxxxx> writes:

> On 10/24/2014 08:18 PM, Eric W. Biederman wrote:

[...]

>> At this point I don't know enough to reproduce this.
>> What does /proc/mounts look like before you start dosemu?
>
> bash-4.2$ cat /proc/mounts
> rootfs / rootfs rw 0 0
> 10.10.0.1:/nfs/root/psion_14.1 / nfs
> rw,relatime,vers=3,rsize=4096,wsize=4096,namlen=255,hard,nolock,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.10.0.1,mountvers=3,mountproto=tcp,local_lock=all,addr=10.10.0.1
> 0 0
> devtmpfs /dev devtmpfs rw,relatime,size=1031016k,nr_inodes=220978,mode=755 0 0
> proc /proc proc rw,relatime 0 0
> sysfs /sys sysfs rw,relatime 0 0
> tmpfs /run tmpfs rw,relatime,mode=755 0 0
> devpts /dev/pts devpts rw,relatime,gid=5,mode=620 0 0
> cgroup /sys/fs/cgroup cgroup rw,relatime,cpu 0 0
> /dev/shm /tmp tmpfs rw,relatime,size=524288k 0 0
> /dev/shm /dev/shm tmpfs rw,relatime,size=524288k 0 0
> nfs:/nfs/usr/slackware-14.1/usr /usr nfs
> ro,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.10.0.1,mountvers=3,mountport=38337,mountproto=udp,local_lock=none,addr=10.10.0.1
> 0 0
> nfs:/nfs/home /home nfs
> rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.10.0.1,mountvers=3,mountport=38337,mountproto=udp,local_lock=none,addr=10.10.0.1
> 0 0
> nfs:/nfs/mp3 /mp3 nfs
> rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.10.0.1,mountvers=3,mountport=38337,mountproto=udp,local_lock=none,addr=10.10.0.1
> 0 0
> nfs:/nfs/src /usr/src nfs
> rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.10.0.1,mountvers=3,mountport=38337,mountproto=udp,local_lock=none,addr=10.10.0.1
> 0 0
> nfs:/nfs/video /video nfs
> rw,relatime,vers=3,rsize=262144,wsize=262144,namlen=255,hard,proto=tcp,timeo=600,retrans=2,sec=sys,mountaddr=10.10.0.1,mountvers=3,mountport=38337,mountproto=udp,local_lock=none,addr=10.10.0.1
> 0 0
>
> I now know why I do not see any file in /usr after running dosemu. The whole
> /usr mount disappears in /proc/mounts. When I remount it I have a usable laptop
> again. Running dosemu a second time does not remove the mount again. In the mean
> time I have seen /usr disappear after running other programs like xterm and
> firefox. But until now never after remouting it.

That is interesting.

It sounds like occassionally your /home mount disappears as well.

Both of those would be consistent with my patch working doing what it
was designed to do.

My guess is that your nfs mount on / is being weird, and causing valid
directory dentries (AKA /usr and /home) to disappear temporariliy, and
it looks like my change is magnifying that weirdness by causing the
mounts on those directory entries to disappear.

What I don't understand is exactly why nfs is being weird that way yet.

I expect what needs to happen is to confirm that nfs directory entry
revalidation is buggy, and at least for the short term re-add the nfs
logic that will avoid dropping a dentry if it is a mount point, or
path to a mount point, to avoid the nfs bugs.

>> My expectation is that you should only see this if the mount points are
>> removed on the nfs server (which does not sound like it is the case).
>
> This is a at home environment with a nfs server in the meter cupboard. I have
> not changed the exports.

On the nfs server doing "rmdir .../nfs/posion_14.1/home" or
"rmdir .../nfs/posion_14.1/usr" should cause the behavior you are
seeing.

As that you aren't doing that something is weird is going on.

>> Although a transient malfunction of the nfs server or misplaced call to
>> check_submounts_and_drop could cause mounts to disappear as well.
>> During testing autofs was observed to have an inappropriate call
>
> I am not using autofs

I mentioned autofs because I think something similar is probably going
on with nfs, as was observed with autofs.

>> to d_invalidate and it is unlikely but possible something like
>> that is going on with nfs as well.
>>
>> Are your nfs mounts read-only or read-write?

> /usr is mounted ro and exported ro

/ is mounted read-write but that seems seems immaterial at the moment.

>> What is your nfs-server and what is it exporting?
>> Which distro are you running?
>
> The nfs-server is slackware64 14.0 with a 3.4 kernel
> part from exports:
> /nfs/usr       -ro,async,no_subtree_check 10.10.0.0/16
>
> The laptop is slackware(32 bit) 14.1 with yesterday's linus kernel
>
>> Which version of dosemu are you running?
>
> 1.4.0.8

Thanks that information helps.

Eric
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