Re: [PATCH] mm/migrate: fix softlockup in do_pages_move() with huge page arrays

["David Hildenbrand (Arm)" <david@kernel.org>]

On 11/7/26 14:38, shao.mingyin@zte.com.cn wrote:
> From: Shao Mingyin <shao.mingyin@zte.com.cn>
> 
> mm/migrate: fix softlockup in do_pages_move() with huge page arrays
> 
> do_pages_move() walks the user page array one page at a time.  For each
> entry it performs two get_user() calls, an mmap_read_lock()/unlock()
> around a folio walk, and an optional store_status(); none of them has to
> sleep when the arrays stay resident and the rwsem is uncontended.
> move_pages_and_store_status() returns early while the page list is
> empty, so an array whose entries all resolve to the same node can run
> the whole loop without any scheduling point.  nr_pages comes straight
> from move_pages(), so a huge array can hold a CPU past the watchdog
> threshold on a non-preemptible kernel; with KASAN and function tracing
> enabled, ten million entries can exceed it.
> 
> Add cond_resched() so that long calls yield periodically.
> do_pages_stat() has the same problem and is being fixed separately.  In
> current mainline only alpha, hexagon and classic m68k can still select
> PREEMPT_NONE, and they cannot enable CONFIG_NUMA, so this mainly
> targets pre-v7.0 stable kernels.

Please share a real kernel splat from a real system.

-- 
Cheers,

David