Messages in this thread Patch in this message | | | Date | Sun, 7 Nov 2010 10:54:33 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [2.6.37-rc1] sys_ioprio_set and RCU locking... |
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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?
Thanx, Paul
> Signed-off-by: Daniel J Blueman <daniel.blueman@gmail.com> > > diff --git a/fs/ioprio.c b/fs/ioprio.c > index 748cfb9..00cc0e5 100644 > --- a/fs/ioprio.c > +++ b/fs/ioprio.c > @@ -139,8 +139,10 @@ SYSCALL_DEFINE3(ioprio_set, int, which, int, who, > int, ioprio) > break; > > do_each_thread(g, p) { > + rcu_read_lock(); > if (__task_cred(p)->uid != who) > continue; > + rcu_read_unlock(); > ret = set_task_ioprio(p, ioprio); > if (ret) > goto free_uid; > @@ -232,8 +234,10 @@ SYSCALL_DEFINE2(ioprio_get, int, which, int, who) > break; > > do_each_thread(g, p) { > + rcu_read_lock(); > if (__task_cred(p)->uid != user->uid) > continue; > + rcu_read_unlock(); > tmpio = get_task_ioprio(p); > if (tmpio < 0) > continue; > -- > Daniel J Blueman > -- > To unsubscribe from this list: send the line "unsubscribe linux-kernel" in > the body of a message to majordomo@vger.kernel.org > More majordomo info at http://vger.kernel.org/majordomo-info.html > Please read the FAQ at http://www.tux.org/lkml/
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