On 04/01/20 at 12:41pm, David Hildenbrand wrote: > With CONFIG_DEFERRED_STRUCT_PAGE_INIT and without CONFIG_PREEMPT, it can > happen that we get RCU stalls detected when booting up. > > [ 60.474005] rcu: INFO: rcu_sched detected stalls on CPUs/tasks: > [ 60.475000] rcu: 1-...0: (0 ticks this GP) idle=02a/1/0x4000000000000000 softirq=1/1 fqs=15000 > [ 60.475000] rcu: (detected by 0, t=60002 jiffies, g=-1199, q=1) > [ 60.475000] Sending NMI from CPU 0 to CPUs 1: > [ 1.760091] NMI backtrace for cpu 1 > [ 1.760091] CPU: 1 PID: 20 Comm: pgdatinit0 Not tainted 4.18.0-147.9.1.el8_1.x86_64 #1 > [ 1.760091] Hardware name: Red Hat KVM, BIOS 1.13.0-1.module+el8.2.0+5520+4e5817f3 04/01/2014 > [ 1.760091] RIP: 0010:__init_single_page.isra.65+0x10/0x4f > [ 1.760091] Code: 48 83 cf 63 48 89 f8 0f 1f 40 00 48 89 c6 48 89 d7 e8 6b 18 80 ff 66 90 5b c3 31 c0 b9 10 00 00 00 49 89 f8 48 c1 e6 33 f3 ab <b8> 07 00 00 00 48 c1 e2 36 41 c7 40 34 01 00 00 00 48 c1 e0 33 41 > [ 1.760091] RSP: 0000:ffffba783123be40 EFLAGS: 00000006 > [ 1.760091] RAX: 0000000000000000 RBX: fffffad34405e300 RCX: 0000000000000000 > [ 1.760091] RDX: 0000000000000000 RSI: 0010000000000000 RDI: fffffad34405e340 > [ 1.760091] RBP: 0000000033f3177e R08: fffffad34405e300 R09: 0000000000000002 > [ 1.760091] R10: 000000000000002b R11: ffff98afb691a500 R12: 0000000000000002 > [ 1.760091] R13: 0000000000000000 R14: 000000003f03ea00 R15: 000000003e10178c > [ 1.760091] FS: 0000000000000000(0000) GS:ffff9c9ebeb00000(0000) knlGS:0000000000000000 > [ 1.760091] CS: 0010 DS: 0000 ES: 0000 CR0: 0000000080050033 > [ 1.760091] CR2: 00000000ffffffff CR3: 000000a1cf20a001 CR4: 00000000003606e0 > [ 1.760091] DR0: 0000000000000000 DR1: 0000000000000000 DR2: 0000000000000000 > [ 1.760091] DR3: 0000000000000000 DR6: 00000000fffe0ff0 DR7: 0000000000000400 > [ 1.760091] Call Trace: > [ 1.760091] deferred_init_pages+0x8f/0xbf > [ 1.760091] deferred_init_memmap+0x184/0x29d > [ 1.760091] ? deferred_free_pages.isra.97+0xba/0xba > [ 1.760091] kthread+0x112/0x130 > [ 1.760091] ? kthread_flush_work_fn+0x10/0x10 > [ 1.760091] ret_from_fork+0x35/0x40 > [ 89.123011] node 0 initialised, 1055935372 pages in 88650ms > > The issue becomes visible when having a lot of memory (e.g., 4TB) > assigned to a single NUMA node - a system that can easily be created > using QEMU. Inside VMs on a hypervisor with quite some memory > overcommit, this is fairly easy to trigger. > > Adding the cond_resched() makes RCU happy. > > Reported-by: Yiqian Wei <yiwei@xxxxxxxxxx> > Cc: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx> > Cc: Kirill Tkhai <ktkhai@xxxxxxxxxxxxx> > Cc: Shile Zhang <shile.zhang@xxxxxxxxxxxxxxxxx> > Cc: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx> > Cc: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx> > Cc: Michal Hocko <mhocko@xxxxxxxxxx> > Cc: Alexander Duyck <alexander.duyck@xxxxxxxxx> > Cc: Baoquan He <bhe@xxxxxxxxxx> > Cc: Oscar Salvador <osalvador@xxxxxxx> > Signed-off-by: David Hildenbrand <david@xxxxxxxxxx> > --- > mm/page_alloc.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/mm/page_alloc.c b/mm/page_alloc.c > index ca1453204e66..084cabffc90d 100644 > --- a/mm/page_alloc.c > +++ b/mm/page_alloc.c > @@ -1877,6 +1877,7 @@ static int __init deferred_init_memmap(void *data) > prev_nr_pages = nr_pages; > pgdat->first_deferred_pfn = spfn; > pgdat_resize_unlock(pgdat, &flags); > + cond_resched(); > goto again; Reviewed-by: Baoquan He <bhe@xxxxxxxxxx>
