1 files changed, 24 insertions, 8 deletions

diff --git a/kernel/user.c b/kernel/user.c
index 89e562feb1b1..d9deae43a9ab 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -13,6 +13,7 @@
 #include <linux/slab.h>
 #include <linux/bitops.h>
 #include <linux/key.h>
+#include <linux/interrupt.h>
 
 /*
  * UID task count cache, to get fast user lookup in "alloc_uid"
@@ -27,6 +28,16 @@
 
 static kmem_cache_t *uid_cachep;
 static struct list_head uidhash_table[UIDHASH_SZ];
+
+/*
+ * The uidhash_lock is mostly taken from process context, but it is
+ * occasionally also taken from softirq/tasklet context, when
+ * task-structs get RCU-freed. Hence all locking must be softirq-safe.
+ * But free_uid() is also called with local interrupts disabled, and running
+ * local_bh_enable() with local interrupts disabled is an error - we'll run
+ * softirq callbacks, and they can unconditionally enable interrupts, and
+ * the caller of free_uid() didn't expect that..
+ */
 static DEFINE_SPINLOCK(uidhash_lock);
 
 struct user_struct root_user = {
@@ -82,15 +93,19 @@ static inline struct user_struct *uid_hash_find(uid_t uid, struct list_head *has
 struct user_struct *find_user(uid_t uid)
 {
         struct user_struct *ret;
+        unsigned long flags;
 
-        spin_lock(&uidhash_lock);
+        spin_lock_irqsave(&uidhash_lock, flags);
         ret = uid_hash_find(uid, uidhashentry(uid));
-        spin_unlock(&uidhash_lock);
+        spin_unlock_irqrestore(&uidhash_lock, flags);
         return ret;
 }
 
 void free_uid(struct user_struct *up)
 {
+        unsigned long flags;
+
+        local_irq_save(flags);
         if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
                 uid_hash_remove(up);
                 key_put(up->uid_keyring);
@@ -98,6 +113,7 @@ void free_uid(struct user_struct *up)
                 kmem_cache_free(uid_cachep, up);
                 spin_unlock(&uidhash_lock);
         }
+        local_irq_restore(flags);
 }
 
 struct user_struct * alloc_uid(uid_t uid)
@@ -105,9 +121,9 @@ struct user_struct * alloc_uid(uid_t uid)
         struct list_head *hashent = uidhashentry(uid);
         struct user_struct *up;
 
-        spin_lock(&uidhash_lock);
+        spin_lock_irq(&uidhash_lock);
         up = uid_hash_find(uid, hashent);
-        spin_unlock(&uidhash_lock);
+        spin_unlock_irq(&uidhash_lock);
 
         if (!up) {
                 struct user_struct *new;
@@ -137,7 +153,7 @@ struct user_struct * alloc_uid(uid_t uid)
                  * Before adding this, check whether we raced
                  * on adding the same user already..
                  */
-                spin_lock(&uidhash_lock);
+                spin_lock_irq(&uidhash_lock);
                 up = uid_hash_find(uid, hashent);
                 if (up) {
                         key_put(new->uid_keyring);
@@ -147,7 +163,7 @@ struct user_struct * alloc_uid(uid_t uid)
                         uid_hash_insert(new, hashent);
                         up = new;
                 }
-                spin_unlock(&uidhash_lock);
+                spin_unlock_irq(&uidhash_lock);
 
         }
         return up;
@@ -183,9 +199,9 @@ static int __init uid_cache_init(void)
                 INIT_LIST_HEAD(uidhash_table + n);
 
         /* Insert the root user immediately (init already runs as root) */
-        spin_lock(&uidhash_lock);
+        spin_lock_irq(&uidhash_lock);
         uid_hash_insert(&root_user, uidhashentry(0));
-        spin_unlock(&uidhash_lock);
+        spin_unlock_irq(&uidhash_lock);
 
         return 0;
 }