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authorIngo Molnar <mingo@elte.hu>2006-01-25 15:23:07 +0100
committerLinus Torvalds <torvalds@g5.osdl.org>2006-01-31 11:30:18 -0800
commit4021cb279a532728c3208a16b9b09b0ca8016850 (patch)
tree1103bc655772ea388eb1fb2b259797bc9c703926
parentd5bee775137c56ed993f1b3c9d66c268b3525d7d (diff)
[PATCH] fix uidhash_lock <-> RCU deadlock
RCU task-struct freeing can call free_uid(), which is taking uidhash_lock - while other users of uidhash_lock are softirq-unsafe. The fix is to always take the uidhash_spinlock in a softirq-safe manner. Signed-off-by: Ingo Molnar <mingo@elte.hu> Acked-by: Paul E. McKenney <paulmck@us.ibm.com> Signed-off-by: Linus Torvalds <torvalds@osdl.org>
-rw-r--r--kernel/user.c25
1 files changed, 17 insertions, 8 deletions
diff --git a/kernel/user.c b/kernel/user.c
index 89e562feb1b..d1ae2349347 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 +28,12 @@
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.
+ */
static DEFINE_SPINLOCK(uidhash_lock);
struct user_struct root_user = {
@@ -83,14 +90,15 @@ struct user_struct *find_user(uid_t uid)
{
struct user_struct *ret;
- spin_lock(&uidhash_lock);
+ spin_lock_bh(&uidhash_lock);
ret = uid_hash_find(uid, uidhashentry(uid));
- spin_unlock(&uidhash_lock);
+ spin_unlock_bh(&uidhash_lock);
return ret;
}
void free_uid(struct user_struct *up)
{
+ local_bh_disable();
if (up && atomic_dec_and_lock(&up->__count, &uidhash_lock)) {
uid_hash_remove(up);
key_put(up->uid_keyring);
@@ -98,6 +106,7 @@ void free_uid(struct user_struct *up)
kmem_cache_free(uid_cachep, up);
spin_unlock(&uidhash_lock);
}
+ local_bh_enable();
}
struct user_struct * alloc_uid(uid_t uid)
@@ -105,9 +114,9 @@ struct user_struct * alloc_uid(uid_t uid)
struct list_head *hashent = uidhashentry(uid);
struct user_struct *up;
- spin_lock(&uidhash_lock);
+ spin_lock_bh(&uidhash_lock);
up = uid_hash_find(uid, hashent);
- spin_unlock(&uidhash_lock);
+ spin_unlock_bh(&uidhash_lock);
if (!up) {
struct user_struct *new;
@@ -137,7 +146,7 @@ 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_bh(&uidhash_lock);
up = uid_hash_find(uid, hashent);
if (up) {
key_put(new->uid_keyring);
@@ -147,7 +156,7 @@ struct user_struct * alloc_uid(uid_t uid)
uid_hash_insert(new, hashent);
up = new;
}
- spin_unlock(&uidhash_lock);
+ spin_unlock_bh(&uidhash_lock);
}
return up;
@@ -183,9 +192,9 @@ 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_bh(&uidhash_lock);
uid_hash_insert(&root_user, uidhashentry(0));
- spin_unlock(&uidhash_lock);
+ spin_unlock_bh(&uidhash_lock);
return 0;
}