Flooding boot logs with
Badness in local_bh_enable at kernel/softirq.c:140
[<c0114272>] local_bh_enable+0x25/0x68
[<c0118015>] collect_signal+0x9e/0xf4
[<c01f3867>] drm_notifier+0x0/0x41
[<c01180c4>] __dequeue_signal+0x59/0x70
[<c0118108>] dequeue_signal+0x2d/0x98
[<c01196bd>] get_signal_to_deliver+0x5b/0x256
[<c0102226>] do_signal+0x51/0xf4
[<c014d4d1>] __pollwait+0x0/0x94
[<c01a8e59>] copy_to_user+0x2d/0x35
[<c014dce4>] sys_select+0x115/0x133
[<c01022f2>] do_notify_resume+0x29/0x37
[<c01024ba>] work_notifysig+0x13/0x19
4021cb279a532728c3208a16b9b09b0ca8016850 is first bad commit
diff-tree 4021cb279a532728c3208a16b9b09b0ca8016850 (from d5bee775137c56ed993f1b3c9d66c268b3525d7d)
Author: Ingo Molnar <[email protected]>
Date: Wed Jan 25 15:23:07 2006 +0100
[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 <[email protected]>
Acked-by: Paul E. McKenney <[email protected]>
Signed-off-by: Linus Torvalds <[email protected]>
:040000 040000 98d3bd6cebd288defc2bee44054d252629e6c020 9319c402e05522b655c2445e9f19cf394b006e02 M kernel
diff --git a/kernel/user.c b/kernel/user.c
index 89e562f..d1ae234 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;
}
-
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