Messages in this thread | | | Date | Thu, 26 Jan 2012 11:26:53 -0800 | From | "Paul E. McKenney" <> | Subject | Re: RCU qsmask !=0 warnings on large-SMP... |
| |
On Thu, Jan 26, 2012 at 04:04:37PM +0100, Steffen Persvold wrote: > On 1/26/2012 02:58, Paul E. McKenney wrote: > >On Wed, Jan 25, 2012 at 11:48:58PM +0100, Steffen Persvold wrote: > [] > > > >This looks like it will produce useful information, but I am not seeing > >output from it below. > > > > Thanx, Paul > > > >>This run it was CPU24 that triggered the issue : > >> > > This line is the printout for the root level : > > >>[ 231.572688] CPU 24, treason uncloaked, rsp @ ffffffff81a1cd80 (rcu_sched), rnp @ ffffffff81a1cd80(r) qsmask=0x1f, c=5132 g=5132 nc=5132 ng=5133 sc=5132 sg=5133 mc=5132 mg=5133
OK, so the rcu_state structure (sc and sg) believes that grace period 5133 has started but not completed, as expected. Strangely enough, so does the root rcu_node structure (nc and ng) and the CPU's leaf rcu_node structure (mc and mg).
The per-CPU rcu_data structure (c and g) does not yet know about the new 5133 grace period, as expected.
So this is the code in kernel/rcutree.c:rcu_start_gp() that does the initialization:
rcu_for_each_node_breadth_first(rsp, rnp) { raw_spin_lock(&rnp->lock); /* irqs already disabled. */ rcu_preempt_check_blocked_tasks(rnp); rnp->qsmask = rnp->qsmaskinit; rnp->gpnum = rsp->gpnum; rnp->completed = rsp->completed; if (rnp == rdp->mynode) rcu_start_gp_per_cpu(rsp, rnp, rdp); rcu_preempt_boost_start_gp(rnp); trace_rcu_grace_period_init(rsp->name, rnp->gpnum, rnp->level, rnp->grplo, rnp->grphi, rnp->qsmask); raw_spin_unlock(&rnp->lock); /* irqs remain disabled. */ }
I am assuming that your debug prints are still invoked right after the raw_spin_lock() above. If so, I would expect nc==ng and mc==mg. Even if your debug prints followed the assignments to rnp->gpnum and rnp->completed, I would expect mc==mg for the root and internal rcu_node structures. But you say below that you get the same values throughout, and in that case, I would expect the leaf rcu_node structure to show something different than the root and internal structures.
The code really does hold the root rcu_node lock at all calls to rcu_gp_start(), so I don't see how we could be getting two CPUs in that code at the same time, which would be one way that the rcu_node and rcu_data structures might get advance notice of the new grace period, but in that case, you would have more than one bit set in ->qsmask.
So, any luck with the trace events for rcu_grace_period and rcu_grace_period_init?
Thanx, Paul
> (this is the WARN_ON printout) : > >>[ 231.576167] ------------[ cut here ]------------ > >>[ 231.576167] WARNING: at kernel/rcutree_plugin.h:1011 rcu_preempt_check_blocked_tasks+0x27/0x30() > >>[ 231.576167] Hardware name: H8QI6 > >>[ 231.576167] Modules linked in: rcutorture > >>[ 231.576167] Pid: 4603, comm: rcu_torture_rea Not tainted 3.2.1-numaconnect10+ #77 > >>[ 231.576167] Call Trace: > >>[ 231.576167]<IRQ> [<ffffffff810bb217>] ? rcu_preempt_check_blocked_tasks+0x27/0x30 > >>[ 231.576167] [<ffffffff8106f47b>] warn_slowpath_common+0x8b/0xc0 > >>[ 231.576167] [<ffffffff8106f4c5>] warn_slowpath_null+0x15/0x20 > >>[ 231.576167] [<ffffffff810bb217>] rcu_preempt_check_blocked_tasks+0x27/0x30 > >>[ 231.576167] [<ffffffff810bb330>] rcu_start_gp+0x110/0x1b0 > >>[ 231.576167] [<ffffffff810bbf3b>] __rcu_process_callbacks+0x8b/0xd0 > >>[ 231.576167] [<ffffffff810bc7a0>] rcu_process_callbacks+0x20/0x40 > >>[ 231.576167] [<ffffffff8107580d>] __do_softirq+0x9d/0x140 > >>[ 231.576167] [<ffffffff815d982c>] call_softirq+0x1c/0x30 > >>[ 231.576167] [<ffffffff8103451a>] do_softirq+0x4a/0x80 > >>[ 231.576167] [<ffffffff81075b83>] irq_exit+0x43/0x60 > >>[ 231.576167] [<ffffffff8104aed5>] smp_apic_timer_interrupt+0x45/0x60 > >>[ 231.576167] [<ffffffff815d834b>] apic_timer_interrupt+0x6b/0x70 > >>[ 231.576167]<EOI> [<ffffffff81067aa9>] ? finish_task_switch+0x59/0xc0 > >>[ 231.576167] [<ffffffff815d4d37>] __schedule+0x337/0x710 > >>[ 231.576167] [<ffffffff81090425>] ? sched_clock_local+0x15/0x80 > >>[ 231.576167] [<ffffffff8107b826>] ? lock_timer_base+0x36/0x70 > >>[ 231.576167] [<ffffffff8107baa2>] ? mod_timer+0xf2/0x1d0 > >>[ 231.576167] [<ffffffffa0001510>] ? rcu_torture_shuffle+0x80/0x80 [rcutorture] > >>[ 231.576167] [<ffffffff815d53ea>] schedule+0x3a/0x60 > >>[ 231.576167] [<ffffffffa0001640>] rcu_torture_reader+0x130/0x230 [rcutorture] > >>[ 231.576167] [<ffffffffa0001dc0>] ? rcu_torture_writer+0x160/0x160 [rcutorture] > >>[ 231.576167] [<ffffffffa0001510>] ? rcu_torture_shuffle+0x80/0x80 [rcutorture] > >>[ 231.576167] [<ffffffff8108a726>] kthread+0x96/0xa0 > >>[ 231.576167] [<ffffffff815d9734>] kernel_thread_helper+0x4/0x10 > >>[ 231.576167] [<ffffffff8108a690>] ? kthread_stop+0x70/0x70 > >>[ 231.576167] [<ffffffff815d9730>] ? gs_change+0xb/0xb > >>[ 231.576167] ---[ end trace 828c8d7afbd02d1b ]--- > >> > > I didn't include the leaf node printout, but the counters were > indentical to the root printout (with the exception of the rnp > address and qsmask of course). > > Cheers, > -- > Steffen Persvold, Chief Architect NumaChip > Numascale AS - www.numascale.com > Tel: +47 92 49 25 54 Skype: spersvold >
| |