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

Mike Rapoport
2026-01-23T08:48:05Z

On Thu, Jan 22, 2026 at 01:43:43PM -0500, Waiman Long 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 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>

Reviewed-by: Mike Rapoport (Microsoft) <rppt@kernel.org>

--
Sincerely yours,
Mike.