Subject: mnt_is_reachable() deadlock? [was: opteron server dies with vserver patch]
From: Pawel Sikora <pluto@pld-linux.org>
Date: Mon, 24 Oct 2011 11:14:05 +0200

 Mon, 24 Oct 2011 11:14:05 +0200
Hi,

i'm comming back with some news about cryptic vserver crash described few months ago
at https://lkml.org/lkml/2011/5/23/398.
decrypted parts from the quite recent crash http://pluto.agmk.net/kernel/vs-crash-3.0.3-vs2.3.1-pre10/
have shown possible
vfs-related deadlock.

git reports some vfs/dcache lock cleanup in the 2.6.38 kernel which exposes pivot root()
deadlock
http://www.spinics.net/lists/linux-fsdevel/msg43078.html fixed in upstream by commit
27cb1572e3e6bb1f8cf6bb3d74c914a87b131792.

it looks like the vserver's mnt is reachable() does the same bad locking scheme as original
pivot root()
and leads to deadlock on my opterons sooner (few minutes) or later (few hours).

for tests i've commented out mnt is reachable() usage and servers works pretty stable
with full load again.
could you please investigate this issue?

BR,
Paweł.