Re: NFSv3 directory traversal causes lockup in 4.9.214

[Bartos-Elekes Zsolt]

Hi!

> I think I found a bug in 4.9.214: a simple directory traversal of a NFSv3-mounted filesystem causes system lockup after 
> a few seconds - everything attempting NFS and local disk access is blocked. The machine is still alive (responding to 
> pings and on the console), but I can't start any new programs.
>
>
> 4.9.213 is OK, 4.9.214 is not.
>
> If we revert commit 67a56e9743171bdacddbdc05a58735aa024bb474 (commit 4b310319c6a8ce708f1033d57145e2aa027a883c upstream), 
> the problem goes away.
>
>
> How to trigger the problem:
>
> mount nfs-server.example.com:/ /mnt/net -o vers=3,ro
> find /mnt/net
>
>
> I have observed this only on two older machines running in i386 mode (my home server, an Intel D2500HN, and a test 
> machine, a Lenovo ThinkCentre A57 (Product ID: 9851-7AG)), but could not trigger the bug on a Pentium III machine (all 
> three running the very same kernel).

I reply to myself: commit dbfc9e9878561da92cdcda41f321137c16966587 ("NFS: Remove superfluous kmap in 
nfs_readdir_xdr_to_array") in 4.9.217 fixes it.

--
Best regards,
Zsolt