mm/mm_init.c | 7 ++++++- 1 file changed, 6 insertions(+), 1 deletion(-)
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 by checking rcu_preempt_depth() as well to prevent calling
cond_resched(). Note that CONFIG_PREEMPT_RCU should always be enabled
in a PREEMPT_RT kernel.
Fixes: 3acb913c9d5b ("mm/mm_init: use deferred_init_memmap_chunk() in deferred_grow_zone()")
Signed-off-by: Waiman Long <longman@redhat.com>
---
mm/mm_init.c | 7 ++++++-
1 file changed, 6 insertions(+), 1 deletion(-)
diff --git a/mm/mm_init.c b/mm/mm_init.c
index fc2a6f1e518f..4d6b6dac6f58 100644
--- a/mm/mm_init.c
+++ b/mm/mm_init.c
@@ -2085,7 +2085,12 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
spfn = chunk_end;
- if (irqs_disabled())
+ /*
+ * pgdat_resize_lock() only disables irqs in non-RT
+ * kernels but calls rcu_read_lock() in a PREEMPT_RT
+ * kernel.
+ */
+ if (irqs_disabled() || rcu_preempt_depth())
touch_nmi_watchdog();
else
cond_resched();
--
2.52.0On Wed, 21 Jan 2026 14:10:36 -0500 Waiman Long <longman@redhat.com> wrote:
> 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 by checking rcu_preempt_depth() as well to prevent calling
> cond_resched(). Note that CONFIG_PREEMPT_RCU should always be enabled
> in a PREEMPT_RT kernel.
>
> ...
>
> --- a/mm/mm_init.c
> +++ b/mm/mm_init.c
> @@ -2085,7 +2085,12 @@ deferred_init_memmap_chunk(unsigned long start_pfn, unsigned long end_pfn,
>
> spfn = chunk_end;
>
> - if (irqs_disabled())
> + /*
> + * pgdat_resize_lock() only disables irqs in non-RT
> + * kernels but calls rcu_read_lock() in a PREEMPT_RT
> + * kernel.
> + */
> + if (irqs_disabled() || rcu_preempt_depth())
> touch_nmi_watchdog();
rcu_preempt_depth() seems a fairly internal low-level thing - it's
rarely used.
Is there a more official way of detecting this condition? Maybe even
#ifdef CONFIG_PREEMPT_RCU?
© 2016 - 2026 Red Hat, Inc.