oom: __task_cred() need rcu_read_lock()
authorKOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Thu, 19 Aug 2010 21:13:39 +0000 (14:13 -0700)
committerLinus Torvalds <torvalds@linux-foundation.org>
Fri, 20 Aug 2010 16:34:55 +0000 (09:34 -0700)
commit8d6c83f0ba5e1bd1e8bb2e3c7de4c276dc247f99
tree58b777adffdaf754b97e6359a325bccdd8919346
parentb52723c5607f7684c2c0c075f86f86da0d7fb6d0
oom: __task_cred() need rcu_read_lock()

dump_tasks() needs to hold the RCU read lock around its access of the
target task's UID.  To this end it should use task_uid() as it only needs
that one thing from the creds.

The fact that dump_tasks() holds tasklist_lock is insufficient to prevent the
target process replacing its credentials on another CPU.

Then, this patch change to call rcu_read_lock() explicitly.

===================================================
[ INFO: suspicious rcu_dereference_check() usage. ]
---------------------------------------------------
mm/oom_kill.c:410 invoked rcu_dereference_check() without protection!

other info that might help us debug this:

rcu_scheduler_active = 1, debug_locks = 1
4 locks held by kworker/1:2/651:
 #0:  (events){+.+.+.}, at: [<ffffffff8106aae7>]
process_one_work+0x137/0x4a0
 #1:  (moom_work){+.+...}, at: [<ffffffff8106aae7>]
process_one_work+0x137/0x4a0
 #2:  (tasklist_lock){.+.+..}, at: [<ffffffff810fafd4>]
out_of_memory+0x164/0x3f0
 #3:  (&(&p->alloc_lock)->rlock){+.+...}, at: [<ffffffff810fa48e>]
find_lock_task_mm+0x2e/0x70

Signed-off-by: KOSAKI Motohiro <kosaki.motohiro@jp.fujitsu.com>
Signed-off-by: David Howells <dhowells@redhat.com>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Acked-by: David Rientjes <rientjes@google.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>
mm/oom_kill.c