mm: vmalloc: replace BUG_ON() by WARN_ON_ONCE()

Currently a vm_unmap_ram() functions triggers a BUG() if an area is not
found.  Replace it by the WARN_ON_ONCE() error message and keep machine
alive instead of stopping it.

The worst case is a memory leaking.

Link: https://lkml.kernel.org/r/[email protected]
Signed-off-by: Uladzislau Rezki (Sony) <[email protected]>
Reviewed-by: Lorenzo Stoakes <[email protected]>
Reviewed-by: Christoph Hellwig <[email protected]>
Cc: Baoquan He <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Christoph Hellwig <[email protected]>
Cc: Matthew Wilcox (Oracle) <[email protected]>
Cc: Nicholas Piggin <[email protected]>
Cc: Oleksiy Avramchenko <[email protected]>
Cc: Roman Gushchin <[email protected]>
Signed-off-by: Andrew Morton <[email protected]>

Author: urezki

mm/vmalloc.c

@@ -2253,7 +2253,9 @@ void vm_unmap_ram(const void *mem, unsigned int count)
 	}
 
 	va = find_unlink_vmap_area(addr);
-	BUG_ON(!va);
+	if (WARN_ON_ONCE(!va))
+		return;
+
 	debug_check_no_locks_freed((void *)va->va_start,
 				    (va->va_end - va->va_start));
 	free_unmap_vmap_area(va);