Messages in this thread | | | Date | Mon, 08 Nov 2010 14:55:46 +0100 | From | Jens Axboe <> | Subject | Re: [2.6.37-rc1] sys_ioprio_set and RCU locking... |
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On 2010-11-08 14:52, Paul E. McKenney wrote: > On Mon, Nov 08, 2010 at 02:28:29PM +0100, Jens Axboe wrote: >> On 2010-11-07 19:54, Paul E. McKenney wrote: >>> On Tue, Nov 02, 2010 at 12:15:30PM +0000, Daniel J Blueman wrote: >>>> With 2.6.37-rc1, I observe sys_ioprio_set not taking the RCU lock [1] >>>> across access to the task credentials. >>>> >>>> Inspecting the code in fs/ioprio.c, the tasklist_lock is held for read >>>> across the __task_cred call, which is presumably sufficient to prevent >>>> the task credentials becoming stale. >>>> >>>> Thus, is there preference to take the RCU lock for read across the >>>> credential access eg at [2], or annotate the call? >>>> >>>> Thanks, >>>> Daniel >>>> >>>> --- [1] >>>> >>>> =================================================== >>>> >>>> [ INFO: suspicious rcu_dereference_check() usage. ] >>>> >>>> --------------------------------------------------- >>>> >>>> kernel/pid.c:419 invoked rcu_dereference_check() without protection! >>>> >>>> >>>> >>>> other info that might help us debug this: >>>> >>>> >>>> >>>> >>>> rcu_scheduler_active = 1, debug_locks = 1 >>>> >>>> 1 lock held by start-stop-daem/2246: >>>> >>>> #0: (tasklist_lock){.?.?..}, at: [<ffffffff811a2dfa>] >>>> sys_ioprio_set+0x8a/0x400 >>>> >>>> >>>> >>>> stack backtrace: >>>> >>>> Pid: 2246, comm: start-stop-daem Not tainted 2.6.37-rc1-330cd+ #2 >>>> >>>> Call Trace: >>>> >>>> [<ffffffff8109f5f4>] lockdep_rcu_dereference+0xa4/0xc0 >>>> >>>> [<ffffffff81085651>] find_task_by_pid_ns+0x81/0x90 >>>> >>>> [<ffffffff8108567d>] find_task_by_vpid+0x1d/0x20 >>>> >>>> [<ffffffff811a3160>] sys_ioprio_set+0x3f0/0x400 >>>> >>>> [<ffffffff816efa79>] ? trace_hardirqs_on_thunk+0x3a/0x3f >>>> >>>> [<ffffffff81003482>] system_call_fastpath+0x16/0x1b >>>> >>>> >>>> --- [2] >>>> >>>> Take the RCU lock for read across acquiring the pointer to the task >>>> credentials and dereferencing it. >>> >>> Jens, does this look sane? >> >> Yes, looks clean enough to me. > > Very good! Are you willing to take the patch in your tree?
Certainly, I'm in the middle of patch monkeying now anyway. Will queue it up.
-- Jens Axboe
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