cgroups: use vmalloc for large cgroups pidlist allocations

Separates all pidlist allocation requests to a separate function that
judges based on the requested size whether or not the array needs to be
vmalloced or can be gotten via kmalloc, and similar for kfree/vfree.

Signed-off-by: Ben Blum <bblum@google.com>
Signed-off-by: Paul Menage <menage@google.com>
Acked-by: Li Zefan <lizf@cn.fujitsu.com>
Cc: Matt Helsley <matthltc@us.ibm.com>
Cc: "Eric W. Biederman" <ebiederm@xmission.com>
Cc: Oleg Nesterov <oleg@redhat.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

1 files changed, 42 insertions, 5 deletions

diff --git a/kernel/cgroup.c b/kernel/cgroup.c
index 97194ba1201..3e356b05b2d 100644
--- a/kernel/cgroup.c
+++ b/kernel/cgroup.c
@@ -50,6 +50,7 @@
 #include <linux/smp_lock.h>
 #include <linux/pid_namespace.h>
 #include <linux/idr.h>
+#include <linux/vmalloc.h> /* TODO: replace with more sophisticated array */
 
 #include <asm/atomic.h>
 
@@ -2351,6 +2352,42 @@ int cgroup_scan_tasks(struct cgroup_scanner *scan)
  */
 
 /*
+ * The following two functions "fix" the issue where there are more pids
+ * than kmalloc will give memory for; in such cases, we use vmalloc/vfree.
+ * TODO: replace with a kernel-wide solution to this problem
+ */
+#define PIDLIST_TOO_LARGE(c) ((c) * sizeof(pid_t) > (PAGE_SIZE * 2))
+static void *pidlist_allocate(int count)
+{
+        if (PIDLIST_TOO_LARGE(count))
+                return vmalloc(count * sizeof(pid_t));
+        else
+                return kmalloc(count * sizeof(pid_t), GFP_KERNEL);
+}
+static void pidlist_free(void *p)
+{
+        if (is_vmalloc_addr(p))
+                vfree(p);
+        else
+                kfree(p);
+}
+static void *pidlist_resize(void *p, int newcount)
+{
+        void *newlist;
+        /* note: if new alloc fails, old p will still be valid either way */
+        if (is_vmalloc_addr(p)) {
+                newlist = vmalloc(newcount * sizeof(pid_t));
+                if (!newlist)
+                        return NULL;
+                memcpy(newlist, p, newcount * sizeof(pid_t));
+                vfree(p);
+        } else {
+                newlist = krealloc(p, newcount * sizeof(pid_t), GFP_KERNEL);
+        }
+        return newlist;
+}
+
+/*
  * pidlist_uniq - given a kmalloc()ed list, strip out all duplicate entries
  * If the new stripped list is sufficiently smaller and there's enough memory
  * to allocate a new buffer, will let go of the unneeded memory. Returns the
@@ -2389,7 +2426,7 @@ after:
          * we'll just stay with what we've got.
          */
         if (PIDLIST_REALLOC_DIFFERENCE(length, dest)) {
-                newlist = krealloc(list, dest * sizeof(pid_t), GFP_KERNEL);
+                newlist = pidlist_resize(list, dest);
                 if (newlist)
                         *p = newlist;
         }
@@ -2470,7 +2507,7 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
          * show up until sometime later on.
          */
         length = cgroup_task_count(cgrp);
-        array = kmalloc(length * sizeof(pid_t), GFP_KERNEL);
+        array = pidlist_allocate(length);
         if (!array)
                 return -ENOMEM;
         /* now, populate the array */
@@ -2494,11 +2531,11 @@ static int pidlist_array_load(struct cgroup *cgrp, enum cgroup_filetype type,
                 length = pidlist_uniq(&array, length);
         l = cgroup_pidlist_find(cgrp, type);
         if (!l) {
-                kfree(array);
+                pidlist_free(array);
                 return -ENOMEM;
         }
         /* store array, freeing old if necessary - lock already held */
-        kfree(l->list);
+        pidlist_free(l->list);
         l->list = array;
         l->length = length;
         l->use_count++;
@@ -2659,7 +2696,7 @@ static void cgroup_release_pid_array(struct cgroup_pidlist *l)
                 /* we're the last user if refcount is 0; remove and free */
                 list_del(&l->links);
                 mutex_unlock(&l->owner->pidlist_mutex);
-                kfree(l->list);
+                pidlist_free(l->list);
                 put_pid_ns(l->key.ns);
                 up_write(&l->mutex);
                 kfree(l);