Re: [PATCH v3 06/10] mm/vma: clean up __vma_enter/exit_locked()

[Andrew Morton <akpm@linux-foundation.org>]

On Thu, 22 Jan 2026 12:15:20 -0800 Suren Baghdasaryan <surenb@google.com> wrote:

> > +       /* vma should remain attached. */
> > +       if (locked)
> > +               WARN_ON_ONCE(__vma_exit_exclusive_locked(vma));
> 
> I'm wary of calling functions from WARN_ON_ONCE() statements. If
> someone decides to replace WARN_ON_ONCE() with VM_WARN_ON_ONCE(), the
> call will disappear when CONFIG_DEBUG_VM=n. Maybe I'm being paranoid
> but it's because I have been bitten by that before...

Yes please.  The elision is desirable if the function has no side-effects, but
__vma_exit_exclusive_locked() changes stuff.

Someone(tm) should check for this.  A pathetically partial grep turns
up plenty of things:

mm/slab_common.c:	if (head && !WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&head_gp_snap)))
mm/slab_common.c:	if (!WARN_ON_ONCE(!poll_state_synchronize_rcu_full(&bnode->gp_snap))) {
mm/page-writeback.c:		WARN_ON_ONCE(atomic_long_add_return(delta,
mm/page_isolation.c:		WARN_ON_ONCE(!pageblock_unisolate_and_move_free_pages(zone, page));
mm/page_alloc.c:	VM_WARN_ONCE(get_pageblock_isolate(page),
mm/numa_memblks.c:	WARN_ON(memblock_clear_hotplug(0, max_addr));
mm/numa_memblks.c:	WARN_ON(memblock_set_node(0, max_addr, &memblock.memory, NUMA_NO_NODE));
mm/numa_memblks.c:	WARN_ON(memblock_set_node(0, max_addr, &memblock.reserved,
mm/zsmalloc.c:		WARN_ON(!zpdesc_trylock(zpdesc));