cpusets: allow empty {cpus,mems}_allowed to be set for unpopulated cpuset

You currently cannot remove all cpus or mems from cpus_allowed or
mems_allowed of a cpuset.  We now allow both if there are no attached
tasks.

Acked-by: Paul Jackson <pj@sgi.com>
Cc: Christoph Lameter <clameter@engr.sgi.com>
Signed-off-by: Paul Menage <menage@google.com>
Signed-off-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 30 insertions, 8 deletions

diff --git a/kernel/cpuset.c b/kernel/cpuset.c
index e6d002fc7392..88b416dfbc72 100644
--- a/kernel/cpuset.c
+++ b/kernel/cpuset.c
@@ -821,11 +821,22 @@ static int update_cpumask(struct cpuset *cs, char *buf)
                 return -EACCES;
 
         trialcs = *cs;
-        retval = cpulist_parse(buf, trialcs.cpus_allowed);
-        if (retval < 0)
-                return retval;
+
+        /*
+         * We allow a cpuset's cpus_allowed to be empty; if it has attached
+         * tasks, we'll catch it later when we validate the change and return
+         * -ENOSPC.
+         */
+        if (!buf[0] || (buf[0] == '\n' && !buf[1])) {
+                cpus_clear(trialcs.cpus_allowed);
+        } else {
+                retval = cpulist_parse(buf, trialcs.cpus_allowed);
+                if (retval < 0)
+                        return retval;
+        }
         cpus_and(trialcs.cpus_allowed, trialcs.cpus_allowed, cpu_online_map);
-        if (cpus_empty(trialcs.cpus_allowed))
+        /* cpus_allowed cannot be empty for a cpuset with attached tasks. */
+        if (atomic_read(&cs->count) && cpus_empty(trialcs.cpus_allowed))
                 return -ENOSPC;
         retval = validate_change(cs, &trialcs);
         if (retval < 0)
@@ -918,16 +929,27 @@ static int update_nodemask(struct cpuset *cs, char *buf)
                 return -EACCES;
 
         trialcs = *cs;
-        retval = nodelist_parse(buf, trialcs.mems_allowed);
-        if (retval < 0)
-                goto done;
+
+        /*
+         * We allow a cpuset's mems_allowed to be empty; if it has attached
+         * tasks, we'll catch it later when we validate the change and return
+         * -ENOSPC.
+         */
+        if (!buf[0] || (buf[0] == '\n' && !buf[1])) {
+                nodes_clear(trialcs.mems_allowed);
+        } else {
+                retval = nodelist_parse(buf, trialcs.mems_allowed);
+                if (retval < 0)
+                        goto done;
+        }
         nodes_and(trialcs.mems_allowed, trialcs.mems_allowed, node_online_map);
         oldmem = cs->mems_allowed;
         if (nodes_equal(oldmem, trialcs.mems_allowed)) {
                 retval = 0;             /* Too easy - nothing to do */
                 goto done;
         }
-        if (nodes_empty(trialcs.mems_allowed)) {
+        /* mems_allowed cannot be empty for a cpuset with attached tasks. */
+        if (atomic_read(&cs->count) && nodes_empty(trialcs.mems_allowed)) {
                 retval = -ENOSPC;
                 goto done;
         }