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authorThomas Gleixner <tglx@linutronix.de>2009-11-02 13:01:56 +0100
committerThomas Gleixner <tglx@linutronix.de>2009-11-02 16:02:39 +0100
commitb00bc0b237055b4c45816325ee14f0bd83e6f590 (patch)
tree8c0e0c31fa3a60834b893c531355a925b7ce454a
parent11df6dddcbc38affb7473aad3d962baf8414a947 (diff)
uids: Prevent tear down race
Ingo triggered the following warning: WARNING: at lib/debugobjects.c:255 debug_print_object+0x42/0x50() Hardware name: System Product Name ODEBUG: init active object type: timer_list Modules linked in: Pid: 2619, comm: dmesg Tainted: G W 2.6.32-rc5-tip+ #5298 Call Trace: [<81035443>] warn_slowpath_common+0x6a/0x81 [<8120e483>] ? debug_print_object+0x42/0x50 [<81035498>] warn_slowpath_fmt+0x29/0x2c [<8120e483>] debug_print_object+0x42/0x50 [<8120ec2a>] __debug_object_init+0x279/0x2d7 [<8120ecb3>] debug_object_init+0x13/0x18 [<810409d2>] init_timer_key+0x17/0x6f [<81041526>] free_uid+0x50/0x6c [<8104ed2d>] put_cred_rcu+0x61/0x72 [<81067fac>] rcu_do_batch+0x70/0x121 debugobjects warns about an enqueued timer being initialized. If CONFIG_USER_SCHED=y the user management code uses delayed work to remove the user from the hash table and tear down the sysfs objects. free_uid is called from RCU and initializes/schedules delayed work if the usage count of the user_struct is 0. The init/schedule happens outside of the uidhash_lock protected region which allows a concurrent caller of find_user() to reference the about to be destroyed user_struct w/o preventing the work from being scheduled. If the next free_uid call happens before the work timer expired then the active timer is initialized and the work scheduled again. The race was introduced in commit 5cb350ba (sched: group scheduling, sysfs tunables) and made more prominent by commit 3959214f (sched: delayed cleanup of user_struct) Move the init/schedule_delayed_work inside of the uidhash_lock protected region to prevent the race. Signed-off-by: Thomas Gleixner <tglx@linutronix.de> Acked-by: Dhaval Giani <dhaval@linux.vnet.ibm.com> Cc: Paul E. McKenney <paulmck@us.ibm.com> Cc: Kay Sievers <kay.sievers@vrfy.org> Cc: stable@kernel.org
-rw-r--r--kernel/user.c2
1 files changed, 1 insertions, 1 deletions
diff --git a/kernel/user.c b/kernel/user.c
index 2c000e7132ac..46d0165ca70c 100644
--- a/kernel/user.c
+++ b/kernel/user.c
@@ -330,9 +330,9 @@ done:
*/
static void free_user(struct user_struct *up, unsigned long flags)
{
- spin_unlock_irqrestore(&uidhash_lock, flags);
INIT_DELAYED_WORK(&up->work, cleanup_user_struct);
schedule_delayed_work(&up->work, msecs_to_jiffies(1000));
+ spin_unlock_irqrestore(&uidhash_lock, flags);
}
#else /* CONFIG_USER_SCHED && CONFIG_SYSFS */