Bug#695872: [squeeze] kernel panic in sunrpc module when using automount daemon

[Jonathan Nieder <jrnieder@gmail.com>]

tags 695872 + upstream patch unreproducible
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Hi Tom,

Tom Downes wrote:

> While running a shell script that looped over a couple hundred
> filesystems accessed via automoutning NFS exports (unmounted prior
> to running the script), there was a kernel panic that prevented
> further automounts from occurring.

Thanks for reporting.

> This problem seems very similar to bug #691764 filed under the
> autofs package but I believe the bug is really in the sunrpc module.

In that report the panic is in different code, so I think they are
distinct.

> I've found a patch described here, applied it to my system and have
> not experienced a crash since. I only ever experienced one crash,
> however, and unpatched systems are yet to crash.

For reference:

  v2.6.38-rc1~407^2~38 kernel panic when mount NFSv4, 2010-12-20

Trond explains:

| The panic place is:
|   rpc_mkpipe
|       __rpc_lookup_create()          <=== find pipefile *idmap*
|       __rpc_mkpipe()                 <=== pipefile is *idmap*
|         __rpc_create_common()
|          ******  BUG_ON(!d_unhashed(dentry)); ****** *panic*
|
| The test is wrong: we can find ourselves with a hashed negative dentry here
| if the idmapper tried to look up the file before we got round to creating
| it.

It seems like a match and I think you're right that the patch would
fix it.  Thanks for finding it.

Hope that helps,
Jonathan