Re: [PATCH v3] vmalloc: Fix accounting with i915

[Michal Hocko <mhocko@suse.com>]

On Wed 11-12-24 20:25:37, Matthew Wilcox wrote:
> If the caller of vmap() specifies VM_MAP_PUT_PAGES (currently only the
> i915 driver), we will decrement nr_vmalloc_pages and MEMCG_VMALLOC in
> vfree().  These counters are incremented by vmalloc() but not by vmap()
> so this will cause an underflow.  Check the VM_MAP_PUT_PAGES flag before
> decrementing either counter.
> 
> Fixes: b944afc9d64d (mm: add a VM_MAP_PUT_PAGES flag for vmap)
> Cc: stable@vger.kernel.org
> Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
> Acked-by: Johannes Weiner <hannes@cmpxchg.org>

Acked-by: Michal Hocko <mhocko@suse.com>
Thanks!

> ---
>  mm/vmalloc.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/vmalloc.c b/mm/vmalloc.c
> index f009b21705c1..5c88d0e90c20 100644
> --- a/mm/vmalloc.c
> +++ b/mm/vmalloc.c
> @@ -3374,7 +3374,8 @@ void vfree(const void *addr)
>  		struct page *page = vm->pages[i];
>  
>  		BUG_ON(!page);
> -		mod_memcg_page_state(page, MEMCG_VMALLOC, -1);
> +		if (!(vm->flags & VM_MAP_PUT_PAGES))
> +			mod_memcg_page_state(page, MEMCG_VMALLOC, -1);
>  		/*
>  		 * High-order allocs for huge vmallocs are split, so
>  		 * can be freed as an array of order-0 allocations
> @@ -3382,7 +3383,8 @@ void vfree(const void *addr)
>  		__free_page(page);
>  		cond_resched();
>  	}
> -	atomic_long_sub(vm->nr_pages, &nr_vmalloc_pages);
> +	if (!(vm->flags & VM_MAP_PUT_PAGES))
> +		atomic_long_sub(vm->nr_pages, &nr_vmalloc_pages);
>  	kvfree(vm->pages);
>  	kfree(vm);
>  }
> -- 
> 2.45.2

-- 
Michal Hocko
SUSE Labs