linux-kernel - Re: BUG in __key_instantiate_and_link(): unable to handle kernel paging request at 0000632e6472616f

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Date:	Mon, 18 Jun 2012 12:11:38 -0400
From:	Bryan Schumaker <bjschuma@...app.com>
To:	Andre Tomt <andre@...t.net>
CC:	"Myklebust, Trond" <Trond.Myklebust@...app.com>,
	"Schumaker, Bryan" <Bryan.Schumaker@...app.com>,
	Linux-NFS <linux-nfs@...r.kernel.org>,
	Fengguang Wu <fengguang.wu@...el.com>,
	David Howells <dhowells@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: BUG in __key_instantiate_and_link(): unable to handle kernel
 paging request at 0000632e6472616f

On 06/18/2012 09:28 AM, Myklebust, Trond wrote:
> On Mon, 2012-06-18 at 11:04 +0200, Andre Tomt wrote:
>> On 16. juni 2012 21:59, Myklebust, Trond wrote:
>>> It looks to me as if the legacy upcall code is assuming that there can
>>> be no more than 1 upcall at a time: there is only a single
>>> idmap->idmap_key_cons, which gets assigned in nfs_idmap_legacy_upcall
>>> and then read in idmap_pipe_downcall.
>>>
>>> Bryan, can you look into this? I suspect that we need a mutex or
>>> something like that (for the legacy upcall case only) to ensure that
>>> nobody overwrites the idmap->idmap_key_cons while an upcall is in
>>> progress.
>>>
>>> Andre, if you want idmapper scalability, then you should rather use the
>>> new idmapper upcall. You need a recent version of the nfs-utils package,
>>> the keyutils package, and they you should add an 'id_resolver' line
>>> to /etc/request-keys.conf as per the nfsidmap manpage.
>>
>> Indeed, using keyutils did avoid the crashes here, 40 hours and counting.
>>
>> Are there any downsides of having keyutils w/ id_resolver on by default 
>> in a distribution? Would it break older kernels or nfs-utils (just not 
>> getting used is fine, obviously)?
> 
> Older kernels aren't able to use the keyutils mechanism, so they will
> still require you to run the idmapd daemon, but there should be no
> problems with just enabling it in /etc/request-key.conf.
> Fedora 17 is supposed to install the id_resolver by default.
> 

Hi Andre,

Can you please check if this patch fixes the old idmapper?

- Bryan

>>From 3bef58765c7308965d06d9e9d7707c7ca55648ee Mon Sep 17 00:00:00 2001
From: Bryan Schumaker <bjschuma@...app.com>
Date: Mon, 18 Jun 2012 12:01:25 -0400
Subject: [PATCH] NFS: Force the legacy idmapper to be single threaded

It was initially coded under the assumption that there would only be one
request at a time, so use a lock to enforce this requirement..

Signed-off-by: Bryan Schumaker <bjschuma@...app.com>
---
 fs/nfs/idmap.c |   13 ++++++++-----
 1 file changed, 8 insertions(+), 5 deletions(-)

diff --git a/fs/nfs/idmap.c b/fs/nfs/idmap.c
index b5b86a0..864c51e 100644
--- a/fs/nfs/idmap.c
+++ b/fs/nfs/idmap.c
@@ -57,6 +57,11 @@ unsigned int nfs_idmap_cache_timeout = 600;
 static const struct cred *id_resolver_cache;
 static struct key_type key_type_id_resolver_legacy;
 
+struct idmap {
+	struct rpc_pipe		*idmap_pipe;
+	struct key_construction	*idmap_key_cons;
+	struct mutex		idmap_mutex;
+};
 
 /**
  * nfs_fattr_init_names - initialise the nfs_fattr owner_name/group_name fields
@@ -310,9 +315,11 @@ static ssize_t nfs_idmap_get_key(const char *name, size_t namelen,
 					    name, namelen, type, data,
 					    data_size, NULL);
 	if (ret < 0) {
+		mutex_lock(&idmap->idmap_mutex);
 		ret = nfs_idmap_request_key(&key_type_id_resolver_legacy,
 					    name, namelen, type, data,
 					    data_size, idmap);
+		mutex_unlock(&idmap->idmap_mutex);
 	}
 	return ret;
 }
@@ -354,11 +361,6 @@ static int nfs_idmap_lookup_id(const char *name, size_t namelen, const char *typ
 /* idmap classic begins here */
 module_param(nfs_idmap_cache_timeout, int, 0644);
 
-struct idmap {
-	struct rpc_pipe		*idmap_pipe;
-	struct key_construction	*idmap_key_cons;
-};
-
 enum {
 	Opt_find_uid, Opt_find_gid, Opt_find_user, Opt_find_group, Opt_find_err
 };
@@ -469,6 +471,7 @@ nfs_idmap_new(struct nfs_client *clp)
 		return error;
 	}
 	idmap->idmap_pipe = pipe;
+	mutex_init(&idmap->idmap_mutex);
 
 	clp->cl_idmap = idmap;
 	return 0;
-- 
1.7.10.4


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