Re: [PATCH v4 3/3] mm: call cond_resched() from deferred_init_memmap()

[Pankaj Gupta]

> Now that deferred pages are initialized with interrupts enabled we can
> replace touch_nmi_watchdog() with cond_resched(), as it was before
> 3a2d7fa8a3d5.
>
> For now, we cannot do the same in deferred_grow_zone() as it is still
> initializes pages with interrupts disabled.
>
> This change fixes RCU problem described:
> linux-mm/20200401104156.11564-2-david@xxxxxxxxxx
>
> [   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
>
> Fixes: 3a2d7fa8a3d5 ("mm: disable interrupts while initializing deferred pages")
> Cc: stable@xxxxxxxxxxxxxxx # 4.17+
>
> Reported-by: Yiqian Wei <yiwei@xxxxxxxxxx>
> Tested-by: David Hildenbrand <david@xxxxxxxxxx>
> Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
> Reviewed-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>
> ---
>  mm/page_alloc.c | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
>
> diff --git a/mm/page_alloc.c b/mm/page_alloc.c
> index 5ffa8d7e5545..deacfe575872 100644
> --- a/mm/page_alloc.c
> +++ b/mm/page_alloc.c
> @@ -1810,7 +1810,7 @@ static int __init deferred_init_memmap(void *data)
>          */
>         while (spfn < epfn) {
>                 nr_pages += deferred_init_maxorder(&i, zone, &spfn, &epfn);
> -               touch_nmi_watchdog();
> +               cond_resched();
>         }
>  zone_empty:
>         /* Sanity check that the next zone really is unpopulated */
> --
> 2.17.1

Reviewed-by: Pankaj Gupta <pankaj.gupta.linux@xxxxxxxxx>

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