Messages in this thread | | | Date | Thu, 23 Oct 2014 21:13:19 +0200 | From | Oleg Nesterov <> | Subject | Re: rcu_preempt detected stalls. |
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On 10/23, Paul E. McKenney wrote: > > On Mon, Oct 13, 2014 at 01:35:04PM -0400, Dave Jones wrote: > > Today in "rcu stall while fuzzing" news: > > > > INFO: rcu_preempt detected stalls on CPUs/tasks: > > Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 > > Tasks blocked on level-0 rcu_node (CPUs 0-3): P766 P646 > > (detected by 0, t=6502 jiffies, g=75434, c=75433, q=0) > > trinity-c342 R running task 13384 766 32295 0x00000000 > > ffff880068943d58 0000000000000002 0000000000000002 ffff880193c8c680 > > 00000000001d4100 0000000000000000 ffff880068943fd8 00000000001d4100 > > ffff88024302c680 ffff880193c8c680 ffff880068943fd8 0000000000000000 > > Call Trace: > > [<ffffffff888368e2>] preempt_schedule_irq+0x52/0xb0 > > [<ffffffff8883df10>] retint_kernel+0x20/0x30 > > [<ffffffff880d9424>] ? lock_acquire+0xd4/0x2b0 > > [<ffffffff8808d495>] ? kill_pid_info+0x5/0x130 > > [<ffffffff8808d4d5>] kill_pid_info+0x45/0x130 > > [<ffffffff8808d495>] ? kill_pid_info+0x5/0x130 > > [<ffffffff8808d6d2>] SYSC_kill+0xf2/0x2f0 > > [<ffffffff8808d67b>] ? SYSC_kill+0x9b/0x2f0 > > [<ffffffff8819c2b7>] ? context_tracking_user_exit+0x57/0x280 > > [<ffffffff880136bd>] ? syscall_trace_enter+0x13d/0x310 > > [<ffffffff8808fd9e>] SyS_kill+0xe/0x10 > > [<ffffffff8883d3a4>] tracesys+0xdd/0xe2 > > Well, there is a loop in kill_pid_info(). I am surprised that it > would loop indefinitely, but if it did, you would certainly get > RCU CPU stalls. Please see patch below, adding Oleg for his thoughts.
Yes, this loops should not be a problem, we only restart if we race with a multi-threaded exec from a non-leader thread.
But I already saw a couple of bug-reports which look as a task_struct corruption (->signal/creds == NULL), looks like something was broken recently. Perhaps an unbalanced put_task_struct...
_Perhaps_ this is another case. If ->sighand was nullified then it will loop forever.
Oleg.
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