Re: NFS Force Unmounting

[NeilBrown <neilb@suse.com>]

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What to people think of the following as an approach
to Joshua's need?

It isn't complete by itself: it needs a couple of changes to
nfs-utils so that it doesn't stat the mountpoint on remount,
and it might need another kernel change so that the "mount" system
call performs the same sort of careful lookup for remount as  the umount
system call does, but those are relatively small details.

This is the patch that you will either love of hate.

With this patch, Joshua (or any other sysadmin) could:

  mount -o remount,retrans=0,timeo=1 /path

and then new requests on any mountpoint from that server will timeout
quickly.
Then
  umount -f /path
  umount -f /path

should kill off any existing requests that use the old timeout. (I just
tested and I did need this twice to kill of an "ls -l".
The first was an 'open' systemcall, then next as 'newfstat'. I wonder
why the getattr for fstat didn't use the new timeout...)

Thoughts?
NeilBrown

diff --git a/fs/nfs/super.c b/fs/nfs/super.c
index c9d24bae3025..ced12fcec349 100644
--- a/fs/nfs/super.c
+++ b/fs/nfs/super.c
@@ -2210,27 +2210,39 @@ static int nfs_validate_text_mount_data(void *options,
 		~(NFS_MOUNT_UNSHARED | NFS_MOUNT_NORESVPORT))
 
 static int
-nfs_compare_remount_data(struct nfs_server *nfss,
-			 struct nfs_parsed_mount_data *data)
+nfs_compare_and_set_remount_data(struct nfs_server *nfss,
+				 struct nfs_parsed_mount_data *data)
 {
 	if ((data->flags ^ nfss->flags) & NFS_REMOUNT_CMP_FLAGMASK ||
 	    data->rsize != nfss->rsize ||
 	    data->wsize != nfss->wsize ||
 	    data->version != nfss->nfs_client->rpc_ops->version ||
 	    data->minorversion != nfss->nfs_client->cl_minorversion ||
-	    data->retrans != nfss->client->cl_timeout->to_retries ||
 	    !nfs_auth_info_match(&data->auth_info, nfss->client->cl_auth->au_flavor) ||
 	    data->acregmin != nfss->acregmin / HZ ||
 	    data->acregmax != nfss->acregmax / HZ ||
 	    data->acdirmin != nfss->acdirmin / HZ ||
 	    data->acdirmax != nfss->acdirmax / HZ ||
-	    data->timeo != (10U * nfss->client->cl_timeout->to_initval / HZ) ||
 	    data->nfs_server.port != nfss->port ||
 	    data->nfs_server.addrlen != nfss->nfs_client->cl_addrlen ||
 	    !rpc_cmp_addr((struct sockaddr *)&data->nfs_server.address,
 			  (struct sockaddr *)&nfss->nfs_client->cl_addr))
 		return -EINVAL;
 
+	if (data->retrans != nfss->client->cl_timeout->to_retries ||
+	    data->timeo != (10U * nfss->client->cl_timeout->to_initval / HZ)) {
+		/* Note that this will affect all mounts from the same server,
+		 * that use the same protocol.  The timeouts are always forced
+		 * to be the same.
+		 */
+		struct rpc_clnt *cl = nfss->client;
+		if (cl->cl_timeout != &cl->cl_timeout_default)
+			memcpy(&cl->cl_timeout_default, cl->cl_timeout,
+			       sizeof(struct rpc_timeout));
+		cl->cl_timeout_default.to_retries = data->retrans;
+		cl->cl_timeout_default.to_initval = data->timeo * HZ / 10U;
+	}
+
 	return 0;
 }
 
@@ -2244,7 +2256,8 @@ nfs_remount(struct super_block *sb, int *flags, char *raw_data)
 	struct nfs4_mount_data *options4 = (struct nfs4_mount_data *)raw_data;
 	u32 nfsvers = nfss->nfs_client->rpc_ops->version;
 
-	sync_filesystem(sb);
+	if (sb->s_readonly_remount)
+		sync_filesystem(sb);
 
 	/*
 	 * Userspace mount programs that send binary options generally send
@@ -2295,7 +2308,7 @@ nfs_remount(struct super_block *sb, int *flags, char *raw_data)
 		*flags |= MS_SYNCHRONOUS;
 
 	/* compare new mount options with old ones */
-	error = nfs_compare_remount_data(nfss, data);
+	error = nfs_compare_and_set_remount_data(nfss, data);
 out:
 	kfree(data);
 	return error;

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