On Thu, 19 Aug 2010, David Howells wrote:
> From: KOSAKI Motohiro <kosaki.motohiro@xxxxxxxxxxxxxx>
>
> 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@xxxxxxxxxxxxxx>
> Signed-off-by: David Howells <dhowells@xxxxxxxxxx>
Acked-by: David Rientjes <rientjes@xxxxxxxxxx>
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