mount -t tmpfs -o mpol=: check nodes online

Randy Dunlap reports that a tmpfs, mounted with NUMA mpol= specifying an
offline node, crashes as soon as data is allocated upon it.  Now restrict it
to online nodes, where before it restricted to MAX_NUMNODES.

Signed-off-by: Hugh Dickins <hugh@veritas.com>
Cc: Robin Holt <holt@sgi.com>
Cc: Christoph Lameter <clameter@sgi.com>
Cc: Andi Kleen <ak@suse.de>
Tested-and-acked-by: Randy Dunlap <randy.dunlap@oracle.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

Documentation/filesystems/tmpfs.txt

@@ -94,10 +94,10 @@ largest node numbers in the range.  For example, mpol=bind:0-3,5,7,9-15
 
 Note that trying to mount a tmpfs with an mpol option will fail if the
 running kernel does not support NUMA; and will fail if its nodelist
-specifies a node >= MAX_NUMNODES.  If your system relies on that tmpfs
+specifies a node which is not online.  If your system relies on that
-being mounted, but from time to time runs a kernel built without NUMA
+tmpfs being mounted, but from time to time runs a kernel built without
-capability (perhaps a safe recovery kernel), or configured to support
+NUMA capability (perhaps a safe recovery kernel), or with fewer nodes
-fewer nodes, then it is advisable to omit the mpol option from automatic
+online, then it is advisable to omit the mpol option from automatic
 mount options.  It can be added later, when the tmpfs is already mounted
 on MountPoint, by 'mount -o remount,mpol=Policy:NodeList MountPoint'.
 
@@ -121,4 +121,4 @@ RAM/SWAP in 10240 inodes and it is only accessible by root.
 Author:
    Christoph Rohland <cr@sap.com>, 1.12.01
 Updated:
-   Hugh Dickins <hugh@veritas.com>, 19 February 2006
+   Hugh Dickins <hugh@veritas.com>, 4 June 2007

mm/shmem.c

@@ -967,6 +967,8 @@ static inline int shmem_parse_mpol(char *value, int *policy, nodemask_t *policy_
 		*nodelist++ = '\0';
 		if (nodelist_parse(nodelist, *policy_nodes))
 			goto out;
+		if (!nodes_subset(*policy_nodes, node_online_map))
+			goto out;
 	}
 	if (!strcmp(value, "default")) {
 		*policy = MPOL_DEFAULT;