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

[Mike Rapoport <rppt@kernel.org>]

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.