On Mon, Feb 08, 2021 at 09:28:24AM -0800, Darrick J. Wong wrote: > On Mon, Feb 09, 2021 at 09:11:40AM -0800, Paul E. McKenney wrote: > > On Mon, Feb 08, 2021 at 10:44:58AM -0500, Brian Foster wrote: > > > On Mon, Feb 08, 2021 at 06:57:24AM -0800, Paul E. McKenney wrote: > > > > On Mon, Feb 08, 2021 at 09:07:24AM -0500, Brian Foster wrote: > > > > > On Fri, Feb 05, 2021 at 09:12:40AM -0800, Paul E. McKenney wrote: > > > > > > On Fri, Feb 05, 2021 at 08:29:06AM +0100, Paul Menzel wrote: > > > > > > > Dear Linux folks, > > > > > > > > > > > > > > > > > > > > > On a Dell PowerEdge T630/0NT78X, BIOS 2.8.0 05/23/2018 with Linux > > > > > > > 5.4.57, we > > > > > > > twice saw a self-detected stall on a CPU (October 27th, 2020, > > > > > > > January 18th, > > > > > > > 2021). > > > > > > > > > > > > > > Both times, the workqueue is `xfs-conv/md0 xfs_end_io`. > > > > > > > > > > > > > > ``` > > > > > > > [ 0.000000] Linux version 5.4.57.mx64.340 > > > > > > > (r...@theinternet.molgen.mpg.de) (gcc version 7.5.0 (GCC)) #1 SMP > > > > > > > Tue Aug 11 > > > > > > > 13:20:33 CEST 2020 > > > > > > > […] > > > > > > > [48962.981257] rcu: INFO: rcu_sched self-detected stall on CPU > > > > > > > [48962.987511] rcu: 4-....: (20999 ticks this GP) > > > > > > > idle=fe6/1/0x4000000000000002 softirq=3630188/3630188 fqs=4696 > > > > > > > [48962.998805] (t=21017 jiffies g=14529009 q=32263) > > > > > > > [48963.004074] Task dump for CPU 4: > > > > > > > [48963.007689] kworker/4:2 R running task 0 25587 > > > > > > > 2 > > > > > > > 0x80004008 > > > > > > > [48963.015591] Workqueue: xfs-conv/md0 xfs_end_io > > > > > > > [48963.020570] Call Trace: > > > > > > > [48963.023311] <IRQ> > > > > > > > [48963.025560] sched_show_task+0x11e/0x150 > > > > > > > [48963.029957] rcu_dump_cpu_stacks+0x70/0xa0 > > > > > > > [48963.034545] rcu_sched_clock_irq+0x502/0x770 > > > > > > > [48963.039322] ? tick_sched_do_timer+0x60/0x60 > > > > > > > [48963.044106] update_process_times+0x24/0x60 > > > > > > > [48963.048791] tick_sched_timer+0x37/0x70 > > > > > > > [48963.053089] __hrtimer_run_queues+0x11f/0x2b0 > > > > > > > [48963.057960] ? recalibrate_cpu_khz+0x10/0x10 > > > > > > > [48963.062744] hrtimer_interrupt+0xe5/0x240 > > > > > > > [48963.067235] smp_apic_timer_interrupt+0x6f/0x130 > > > > > > > [48963.072407] apic_timer_interrupt+0xf/0x20 > > > > > > > [48963.076994] </IRQ> > > > > > > > [48963.079347] RIP: 0010:_raw_spin_unlock_irqrestore+0xa/0x10 > > > > > > > [48963.085491] Code: f3 90 83 e8 01 75 e8 65 8b 3d 42 0f 56 7e e8 > > > > > > > ed ea 5e > > > > > > > ff 48 29 e8 4c 39 e8 76 cf 80 0b 08 eb 8c 0f 1f 44 00 00 c6 07 00 > > > > > > > 56 9d <c3> > > > > > > > 0f 1f 44 00 00 0f 1f 44 00 00 b8 00 fe ff ff f0 0f c1 07 56 9d > > > > > > > [48963.106524] RSP: 0018:ffffc9000738fd40 EFLAGS: 00000202 > > > > > > > ORIG_RAX: > > > > > > > ffffffffffffff13 > > > > > > > [48963.115003] RAX: ffffffff82407588 RBX: ffffffff82407580 RCX: > > > > > > > ffffffff82407588 > > > > > > > [48963.122994] RDX: ffffffff82407588 RSI: 0000000000000202 RDI: > > > > > > > ffffffff82407580 > > > > > > > [48963.130989] RBP: 0000000000000202 R08: ffffffff8203ea00 R09: > > > > > > > 0000000000000001 > > > > > > > [48963.138982] R10: ffffc9000738fbb8 R11: 0000000000000001 R12: > > > > > > > ffffffff82407588 > > > > > > > [48963.146976] R13: ffffea005e7ae600 R14: ffff8897b7e5a040 R15: > > > > > > > ffffea005e7ae600 > > > > > > > [48963.154971] wake_up_page_bit+0xe0/0x100 > > > > > > > [48963.159366] xfs_destroy_ioend+0xce/0x1c0 > > > > > > > [48963.163857] xfs_end_ioend+0xcf/0x1a0 > > > > > > > [48963.167958] xfs_end_io+0xa4/0xd0 > > > > > > > [48963.171672] process_one_work+0x1e5/0x410 > > > > > > > [48963.176163] worker_thread+0x2d/0x3c0 > > > > > > > [48963.180265] ? cancel_delayed_work+0x90/0x90 > > > > > > > [48963.185048] kthread+0x117/0x130 > > > > > > > [48963.188663] ? kthread_create_worker_on_cpu+0x70/0x70 > > > > > > > [48963.194321] ret_from_fork+0x35/0x40 > > > > > > > ``` > > > > > > > > > > > > > > As it’s just log level INFO, is there anything what should be > > > > > > > done, or was > > > > > > > the system probably just “overloaded”? > > > > > > > > > > > > I am assuming that you are building your kernel with > > > > > > CONFIG_PREEMPT_NONE=y > > > > > > rather than CONFIG_PREEMPT_VOLUNTARY=y. > > > > > > > > > > > > If so, and if the problem is that you are temporarily overdriving > > > > > > xfs I/O, > > > > > > one approach would be as follows: > > > > > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > > > > > diff --git a/fs/xfs/xfs_aops.c b/fs/xfs/xfs_aops.c > > > > > > index f16d5f1..06be426 100644 > > > > > > --- a/fs/xfs/xfs_aops.c > > > > > > +++ b/fs/xfs/xfs_aops.c > > > > > > @@ -390,6 +390,7 @@ xfs_end_io( > > > > > > list_del_init(&ioend->io_list); > > > > > > xfs_ioend_try_merge(ioend, &completion_list); > > > > > > xfs_end_ioend(ioend); > > > > > > + cond_resched(); > > > > > > } > > > > > > } > > > > > > > > > > > > ------------------------------------------------------------------------ > > > > > > > > > > FWIW, this looks quite similar to the problem I attempted to fix with > > > > > these patches: > > > > > > > > > > https://lore.kernel.org/linux-xfs/20201002153357.56409-1-bfos...@redhat.com/ > > > > > > > > Looks plausible to me! Do you plan to re-post taking the feedback > > > > into account? > > > > > > There was a v2 inline that incorporated some directed feedback. > > > Otherwise there were questions and ideas about making the whole thing > > > faster, but I've no idea if that addresses the problem or not (if so, > > > that would be an entirely different set of patches). I'll wait and see > > > what Darrick thinks about this and rebase/repost if the approach is > > > agreeable.. > > > > There is always the school of thought that says that the best way to > > get people to focus on this is to rebase and repost. Otherwise, they > > are all too likely to assume that you lost interest in this. > > I was hoping that a better solution would emerge for clearing > PageWriteback on hundreds of thousands of pages, but nothing easy popped > out. > > The hardcoded threshold in "[PATCH v2 2/2] xfs: kick extra large ioends > to completion workqueue" gives me unease because who's to say if marking > 262,144 pages on a particular CPU will actually stall it long enough to > trip the hangcheck? Is the number lower on (say) some pokey NAS box > with a lot of storage but a slow CPU? > > That said, /some/ threshold is probably better than no threshold. Could > someone try to confirm if that series of Brian's fixes this problem too? >
Note that this particular report looks like it's already in wq context, so patch 1 by itself might be sufficient... Brian > --D > > > Thanx, Paul > > > > > Brian > > > > > > > Thanx, Paul > > > > > > > > > Brian > > > > > > > > > > > > > > > > > If you have instead built with CONFIG_PREEMPT_VOLUNTARY=y, then your > > > > > > problem is likely massive lock contention in wake_up_page_bit(), or > > > > > > perhaps someone having failed to release that lock. The usual way > > > > > > to > > > > > > work this out is by enabling lockdep (CONFIG_PROVE_LOCKING=y), but > > > > > > this > > > > > > is often not what you want enabled in production. > > > > > > > > > > > > Darrick, thoughts from an xfs perspective? > > > > > > > > > > > > Thanx, Paul > > > > > > > > > > > > > > > > > > >
