On Wed, 26 Jul 2017 18:42:14 -0700 "Paul E. McKenney" <paul...@linux.vnet.ibm.com> wrote:
> On Wed, Jul 26, 2017 at 04:22:00PM -0700, David Miller wrote: > > Indeed, that really wouldn't explain how we end up with a RCU stall > > dump listing almost all of the cpus as having missed a grace period. > > I have seen stranger things, but admittedly not often. So the backtraces show the RCU gp thread in schedule_timeout. Are you sure that it's timeout has expired and it's not being scheduled, or could it be a bad (large) timeout (looks unlikely) or that it's being scheduled but not correctly noting gps on other CPUs? It's not in R state, so if it's not being scheduled at all, then it's because the timer has not fired: [ 1984.628602] rcu_preempt kthread starved for 5663 jiffies! g1566 c1565 f0x0 RCU_GP_WAIT_FQS(3) ->state=0x1 [ 1984.638153] rcu_preempt S 0 9 2 0x00000000 [ 1984.643626] Call trace: [ 1984.646059] [<ffff000008084fb0>] __switch_to+0x90/0xa8 [ 1984.651189] [<ffff000008962274>] __schedule+0x19c/0x5d8 [ 1984.656400] [<ffff0000089626e8>] schedule+0x38/0xa0 [ 1984.661266] [<ffff000008965844>] schedule_timeout+0x124/0x218 [ 1984.667002] [<ffff000008121424>] rcu_gp_kthread+0x4fc/0x748 [ 1984.672564] [<ffff0000080df0b4>] kthread+0xfc/0x128 [ 1984.677429] [<ffff000008082ec0>] ret_from_fork+0x10/0x50
