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/20221222190022.134380-3-urezki@gmail.com
Signed-off-by: Uladzislau Rezki (Sony) <urezki@gmail.com>
Reviewed-by: Lorenzo Stoakes <lstoakes@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Cc: Baoquan He <bhe@redhat.com>
Cc: Christoph Hellwig <hch@infradead.org>
Cc: Christoph Hellwig <hch@lst.de>
Cc: Matthew Wilcox (Oracle) <willy@infradead.org>
Cc: Nicholas Piggin <npiggin@gmail.com>
Cc: Oleksiy Avramchenko <oleksiy.avramchenko@sony.com>
Cc: Roman Gushchin <roman.gushchin@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>

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);