[PATCH v3] vmalloc: Fix accounting with i915

["Matthew Wilcox (Oracle)" <willy@infradead.org>]

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>
---
 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