dm: always update the array size in realloc_argv on success

realloc_argv() was only updating the array size if it was called with
old_argv already allocated. The first time it was called to create an
argv array, it would allocate the array but return the array size as
zero. dm_split_args() would think that it couldn't store any arguments
in the array and would call realloc_argv() again, causing it to
reallocate the initial slots (this time using GPF_KERNEL) and finally
return a size. Aside from being wasteful, this could cause deadlocks on
targets that need to process messages without starting new IO. Instead,
realloc_argv should always update the allocated array size on success.

Fixes: a065192 ("dm table: don't copy from a NULL pointer in realloc_argv()")
Cc: stable@vger.kernel.org
Signed-off-by: Benjamin Marzinski <bmarzins@redhat.com>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>

drivers/md/dm-table.c

@@ -523,9 +523,10 @@ static char **realloc_argv(unsigned int *size, char **old_argv)
 		gfp = GFP_NOIO;
 	}
 	argv = kmalloc_array(new_size, sizeof(*argv), gfp);
-	if (argv && old_argv) {
-		memcpy(argv, old_argv, *size * sizeof(*argv));
+	if (argv) {
 		*size = new_size;
+		if (old_argv)
+			memcpy(argv, old_argv, *size * sizeof(*argv));
 	}
 
 	kfree(old_argv);