Messages in this thread | | | Date | Thu, 23 Oct 2014 12:38:07 -0700 | From | "Paul E. McKenney" <> | Subject | Re: rcu_preempt detected stalls. |
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On Thu, Oct 23, 2014 at 09:13:19PM +0200, Oleg Nesterov wrote: > 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.
OK, so making each pass through the loop a separate RCU read-side critical section might be considered to be suppressing notification of an error condition?
Thanx, Paul
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