[PATCH v3] mm/mm_init: Don't cond_resched() in deferred_init_memmap_chunk() if called from deferred_grow_zone()

Waiman Long
2026-01-22T18:44:34Z

Commit 3acb913c9d5b ("mm/mm_init: use deferred_init_memmap_chunk()
in deferred_grow_zone()") made deferred_grow_zone() call
deferred_init_memmap_chunk() within a pgdat_resize_lock() critical
section with irqs disabled. It did check for irqs_disabled() in
deferred_init_memmap_chunk() to avoid calling cond_resched(). For a
PREEMPT_RT kernel build, however, spin_lock_irqsave() does not disable
interrupt but rcu_read_lock() is called. This leads to the following
bug report.

BUG: sleeping function called from invalid context at mm/mm_init.c:2091
in_atomic(): 0, irqs_disabled(): 0, non_block: 0, pid: 1, name: swapper/0
preempt_count: 0, expected: 0
RCU nest depth: 1, expected: 0
3 locks held by swapper/0/1:
#0: ffff80008471b7a0 (sched_domains_mutex){+.+.}-{4:4}, at: sched_domains_mutex_lock+0x28/0x40
#1: ffff003bdfffef48 (&pgdat->node_size_lock){+.+.}-{3:3}, at: deferred_grow_zone+0x140/0x278
#2: ffff800084acf600 (rcu_read_lock){....}-{1:3}, at: rt_spin_lock+0x1b4/0x408
CPU: 0 UID: 0 PID: 1 Comm: swapper/0 Tainted: G W 6.19.0-rc6-test #1 PREEMPT_{RT,(full)
}
Tainted: [W]=WARN
Call trace:
show_stack+0x20/0x38 (C)
dump_stack_lvl+0xdc/0xf8
dump_stack+0x1c/0x28
__might_resched+0x384/0x530
deferred_init_memmap_chunk+0x560/0x688
deferred_grow_zone+0x190/0x278
_deferred_grow_zone+0x18/0x30
get_page_from_freelist+0x780/0xf78
__alloc_frozen_pages_noprof+0x1dc/0x348
alloc_slab_page+0x30/0x110
allocate_slab+0x98/0x2a0
new_slab+0x4c/0x80
___slab_alloc+0x5a4/0x770
__slab_alloc.constprop.0+0x88/0x1e0
__kmalloc_node_noprof+0x2c0/0x598
__sdt_alloc+0x3b8/0x728
build_sched_domains+0xe0/0x1260
sched_init_domains+0x14c/0x1c8
sched_init_smp+0x9c/0x1d0
kernel_init_freeable+0x218/0x358
kernel_init+0x28/0x208
ret_from_fork+0x10/0x20

Fix it adding a new argument to deferred_init_memmap_chunk() to
explicitly tell it if cond_resched() is allowed or not instead of
relying on some current state information which may vary depending
on the exact kernel configuration options that are enabled.

Fixes: 3acb913c9d5b ("mm/mm_init: use deferred_init_memmap_chunk() in deferred_grow_zone()")
Suggested-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Signed-off-by: Waiman Long <longman@redhat.com>
---

[v3]: Add a new can_resched argument to deferred_init_memmap_chunk() as
suggested by Sebastian.

mm/mm_init.c | 12 ++++++------
1 file changed, 6 insertions(+), 6 deletions(-)

diff --git a/mm/mm_init.c b/mm/mm_init.c
index fc2a6f1e518f..2a809cd8e7fa 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -2059,7 +2059,7 @@ static unsigned long __init deferred_init_pages(struct zone *zone,
*/
static unsigned long __init
deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
- struct zone *zone)
+ struct zone *zone, bool can_resched)
{
int nid = zone_to_nid(zone);
unsigned long nr_pages = 0;
@@ -2085,10 +2085,10 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,

spfn = chunk_end;

- if (irqs_disabled())
- touch_nmi_watchdog();
- else
+ if (can_resched)
cond_resched();
+ else
+ touch_nmi_watchdog();
}
}

@@ -2101,7 +2101,7 @@ deferred_init_memmap_job(unsigned long start_pfn, unsigned long end_pfn,
{
struct zone *zone = arg;

- deferred_init_memmap_chunk(start_pfn, end_pfn, zone);
+ deferred_init_memmap_chunk(start_pfn, end_pfn, zone, true);
}

static unsigned int __init
@@ -2216,7 +2216,7 @@ bool __init deferred_grow_zone(struct zone *zone, unsigned int order)
for (spfn = first_deferred_pfn, epfn = SECTION_ALIGN_UP(spfn + 1);
nr_pages < nr_pages_needed && spfn < zone_end_pfn(zone);
spfn = epfn, epfn += PAGES_PER_SECTION) {
- nr_pages += deferred_init_memmap_chunk(spfn, epfn, zone);
+ nr_pages += deferred_init_memmap_chunk(spfn, epfn, zone, false);
}

/*
--
2.52.0