Re: [PATCH v2] mm: fix vma_start_write_killable() signal handling

[Vlastimil Babka <vbabka@suse.cz>]

On 11/26/25 23:09, Matthew Wilcox wrote:
> On Wed, Nov 26, 2025 at 08:33:47PM +0000, Lorenzo Stoakes wrote:
>> 	if (refcount_sub_and_test(VMA_LOCK_OFFSET, &vma->vm_refcnt)) {
>> 		/*
>> 		 * If the VMA is now detached which means we lost a race.
>> 		 * Let the caller know the VMA is detached.
>> 		 */
>> 		err = 0;
>> 	}
>> 
>> That gives a _lot_ more information, keeps it relatively top-level, doesn't
>> make undue assumptions etc.
> 
> Here's what I now have:
> 
>         if (err) {
>                 if (refcount_sub_and_test(VMA_LOCK_OFFSET, &vma->vm_refcnt)) {
>                         /*
>                          * The wait failed, but the last reader went away
>                          * as well.  Tell the caller the VMA is detached.
>                          */
>                         WARN_ON_ONCE(!detaching);
>                         err = 0;
>                 }

Reviewed-by: Vlastimil Babka <vbabka@suse.cz>
Thanks.

> 
>> > Are you satisfied with the WARN_ON(!detaching)?
>> >
>> 
>> It'd be super weird to reach that code when not detaching so sure, think it
>> should be VM_WARN_ON() though since the code would be horribly broken if
>> that was not the case already no?
> 
> The other places in this file are WARN_ON_ONCE rather than VM_WARN*, so
> keep it consistent.