On Fri, Dec 12, 2014 at 11:14:06AM -0800, Linus Torvalds wrote: > On Fri, Dec 12, 2014 at 10:54 AM, Dave Jones <da...@redhat.com> wrote: > > > > Something that's still making me wonder if it's some kind of hardware > > problem is the non-deterministic nature of this bug. > > I'd expect it to be a race condition, though. Which can easily cause > these kinds of issues, and the timing will be pretty random even if > the load is very regular. > > And we know that the scheduler has an integer overflow under Sasha's > loads, although I didn't hear anything from Ingo and friends about it. > Ingo/Peter, you were cc'd on that report, where at least one of the > multiplcations in wake_affine() ended up overflowing.. > > Some scheduler thing that overflows only under heavy load, and screws > up scheduling could easily account for the RCU thread thing. I see it > *less* easily accounting for DaveJ's case, though, because the > watchdog is running at RT priority, and the scheduler would have to > screw up much more to then not schedule an RT task, but.. > > I'm also not sure if the bug ever happens with preemption disabled.
Bah, so I see some watchdog traces with preemption off, and that then taints the kernel, and the fuzzing stops. I'll hack something up so it ignores the taint and keeps going. All I really care about here is the "machine hangs completely" case, which the trace below didn't hit.. (back to fuzzing almost everything, not just lsetxattr btw) [34917.468470] WARNING: CPU: 1 PID: 9226 at kernel/watchdog.c:317 watchdog_overflow_callback+0x9c/0xd0() [34917.468500] Watchdog detected hard LOCKUP on cpu 1 [34917.468516] CPU: 1 PID: 9226 Comm: trinity-c107 Not tainted 3.18.0+ #102 [34917.468542] [loadavg: 155.62 139.10 140.12 10/405 11756] [34917.468559] ffffffff81a65d99 000000005606cf60 ffff880244205b98 ffffffff817c4f75 [34917.468591] ffffffff810cd5a1 ffff880244205bf0 ffff880244205bd8 ffffffff81077cb1 [34917.468623] ffff880244205bd8 ffff880243c55388 0000000000000000 ffff880244205d30 [34917.468655] Call Trace: [34917.468667] <NMI> [<ffffffff817c4f75>] dump_stack+0x4e/0x68 [34917.468696] [<ffffffff810cd5a1>] ? console_unlock+0x1f1/0x4e0 [34917.468718] [<ffffffff81077cb1>] warn_slowpath_common+0x81/0xa0 [34917.468740] [<ffffffff81077d25>] warn_slowpath_fmt+0x55/0x70 [34917.468761] [<ffffffff817c3710>] ? __slab_alloc+0x3c4/0x58f [34917.468783] [<ffffffff8112bce0>] ? restart_watchdog_hrtimer+0x60/0x60 [34917.468806] [<ffffffff8112bd7c>] watchdog_overflow_callback+0x9c/0xd0 [34917.468830] [<ffffffff8116ebed>] __perf_event_overflow+0x9d/0x2a0 [34917.468856] [<ffffffff8116d7c3>] ? perf_event_update_userpage+0x103/0x180 [34917.469785] [<ffffffff8116d6c0>] ? perf_event_task_disable+0x90/0x90 [34917.470705] [<ffffffff8116f7c4>] perf_event_overflow+0x14/0x20 [34917.471632] [<ffffffff8101e749>] intel_pmu_handle_irq+0x1f9/0x3f0 [34917.472553] [<ffffffff81017cbb>] perf_event_nmi_handler+0x2b/0x50 [34917.473459] [<ffffffff81007330>] nmi_handle+0xc0/0x1b0 [34917.474355] [<ffffffff81007275>] ? nmi_handle+0x5/0x1b0 [34917.475245] [<ffffffff8100761a>] default_do_nmi+0x4a/0x140 [34917.476128] [<ffffffff810077d0>] do_nmi+0xc0/0x100 [34917.477012] [<ffffffff817d237a>] end_repeat_nmi+0x1e/0x2e [34917.477902] [<ffffffff81383a37>] ? debug_check_no_obj_freed+0xe7/0x250 [34917.478788] [<ffffffff81383a37>] ? debug_check_no_obj_freed+0xe7/0x250 [34917.479660] [<ffffffff81383a37>] ? debug_check_no_obj_freed+0xe7/0x250 [34917.480523] <<EOE>> [<ffffffff8117b87f>] free_pages_prepare+0x1af/0x240 [34917.481396] [<ffffffff8117dd51>] __free_pages_ok+0x21/0x100 [34917.482270] [<ffffffff8117de4b>] free_compound_page+0x1b/0x20 [34917.483144] [<ffffffff81184d23>] __put_compound_page+0x23/0x30 [34917.484022] [<ffffffff81184da8>] put_compound_page+0x48/0x2e0 [34917.484895] [<ffffffff811854d9>] release_pages+0x239/0x270 [34917.485768] [<ffffffff811b9d1d>] free_pages_and_swap_cache+0x8d/0xa0 [34917.486648] [<ffffffff811a25d4>] tlb_flush_mmu_free+0x34/0x60 [34917.487530] [<ffffffff811a4021>] unmap_single_vma+0x6d1/0x900 [34917.488405] [<ffffffff811a4d51>] unmap_vmas+0x51/0xa0 [34917.489277] [<ffffffff811ae175>] exit_mmap+0xe5/0x1a0 [34917.490143] [<ffffffff81074d6b>] mmput+0x6b/0x100 [34917.490995] [<ffffffff810792ae>] do_exit+0x29e/0xb60 [34917.491823] [<ffffffff8107abfc>] do_group_exit+0x4c/0xc0 [34917.492645] [<ffffffff8107ac84>] SyS_exit_group+0x14/0x20 [34917.493462] [<ffffffff817d0589>] tracesys_phase2+0xd4/0xd9 [34917.494268] ---[ end trace c48441b18b6523a2 ]--- [34917.495171] INFO: NMI handler (perf_event_nmi_handler) took too long to run: 26.690 msecs [34917.496031] perf interrupt took too long (211387 > 5000), lowering kernel.perf_event_max_sample_rate to 25000 [34967.056860] INFO: rcu_sched detected stalls on CPUs/tasks: [34967.057898] 1: (0 ticks this GP) idle=b4c/0/0 softirq=2168971/2168971 [34967.058900] (detected by 2, t=6002 jiffies, g=1058044, c=1058043, q=0) [34967.059867] Task dump for CPU 1: [34967.060827] swapper/1 R running task 14576 0 1 0x00200000 [34967.061802] 0000000142b4be38 4a979bec19cdc3d2 ffffe8ffff003200 0000000000000003 [34967.062786] ffffffff81cb1b80 0000000000000001 ffff880242b4be88 ffffffff8165ff65 [34967.063759] 00001fcecca713d2 ffffffff81cb1ca0 ffffffff81cb1b80 ffffffff81d215b0 [34967.064721] Call Trace: [34967.065649] [<ffffffff8165ff65>] ? cpuidle_enter_state+0x55/0x190 [34967.066570] [<ffffffff81660157>] ? cpuidle_enter+0x17/0x20 [34967.067498] [<ffffffff810bd6c5>] ? cpu_startup_entry+0x355/0x410 [34967.068425] [<ffffffff8103016a>] ? start_secondary+0x1aa/0x230 [35027.731690] INFO: rcu_sched detected stalls on CPUs/tasks: [35027.732701] 1: (0 ticks this GP) idle=b82/0/0 softirq=2168971/2168971 [35027.733652] (detected by 2, t=6002 jiffies, g=1058047, c=1058046, q=0) [35027.734593] Task dump for CPU 1: [35027.735514] swapper/1 R running task 14576 0 1 0x00200000 [35027.736445] 0000000142b4be38 4a979bec19cdc3d2 ffffe8ffff003200 0000000000000004 [35027.737369] ffffffff81cb1b80 0000000000000001 ffff880242b4be88 ffffffff8165ff65 [35027.738285] 00001fde808fc8c8 ffffffff81cb1cf8 ffffffff81cb1b80 ffffffff81d215b0 [35027.739206] Call Trace: [35027.740114] [<ffffffff8165ff65>] ? cpuidle_enter_state+0x55/0x190 [35027.741032] [<ffffffff81660157>] ? cpuidle_enter+0x17/0x20 [35027.741949] [<ffffffff810bd6c5>] ? cpu_startup_entry+0x355/0x410 [35027.742858] [<ffffffff8103016a>] ? start_secondary+0x1aa/0x230 [35982.698415] perf interrupt took too long (209762 > 10000), lowering kernel.perf_event_max_sample_rate to 12500 [37306.241794] perf interrupt took too long (208160 > 19841), lowering kernel.perf_event_max_sample_rate to 6300 [38626.487390] perf interrupt took too long (206565 > 39062), lowering kernel.perf_event_max_sample_rate to 3200 [39781.429034] perf interrupt took too long (204990 > 78125), lowering kernel.perf_event_max_sample_rate to 1600 [41041.380281] perf interrupt took too long (203427 > 156250), lowering kernel.perf_event_max_sample_rate to 800 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
