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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. This is probably in the same spirit as the do_pages_stat() patch[1][2]. [1] https://lore.kernel.org/all/20261031033330.3416326-1-xiqi5703@163.com/ [2] https://lore.kernel.org/all/20261103080557.1632382-1-xiqi5703@163.com/ > > Fixes: a49bd4d71637 ("mm, numa: rework do_pages_move") > Cc: stable@vger.kernel.org > Signed-off-by: Shao Mingyin > --- > mm/migrate.c | 2 ++ > 1 file changed, 2 insertions(+) > > diff --git a/mm/migrate.c b/mm/migrate.c > index 875079464930..3122ecb85270 100644 > --- a/mm/migrate.c > +++ b/mm/migrate.c > @@ -2372,6 +2372,8 @@ static int do_pages_move(struct mm_struct *mm, node= mask_t task_nodes, > const void __user *p; > int node; > =20 > + cond_resched(); > + > err =3D -EFAULT; > if (in_compat_syscall()) { > compat_uptr_t cp; --=20 Best Regards, Yan, Zi