module: Annotate module version magic

Due to the new lockdep checks in the coming patch, we go:

[    9.759380] ------------[ cut here ]------------
[    9.759389] WARNING: CPU: 31 PID: 597 at ../kernel/module.c:216 each_symbol_section+0x121/0x130()
[    9.759391] Modules linked in:
[    9.759393] CPU: 31 PID: 597 Comm: modprobe Not tainted 4.0.0-rc1+ #65
[    9.759393] Hardware name: Intel Corporation S2600GZ/S2600GZ, BIOS SE5C600.86B.02.02.0002.122320131210 12/23/2013
[    9.759396]  ffffffff817d8676 ffff880424567ca8 ffffffff8157e98b 0000000000000001
[    9.759398]  0000000000000000 ffff880424567ce8 ffffffff8105fbc7 ffff880424567cd8
[    9.759400]  0000000000000000 ffffffff810ec160 ffff880424567d40 0000000000000000
[    9.759400] Call Trace:
[    9.759407]  [<ffffffff8157e98b>] dump_stack+0x4f/0x7b
[    9.759410]  [<ffffffff8105fbc7>] warn_slowpath_common+0x97/0xe0
[    9.759412]  [<ffffffff810ec160>] ? section_objs+0x60/0x60
[    9.759414]  [<ffffffff8105fc2a>] warn_slowpath_null+0x1a/0x20
[    9.759415]  [<ffffffff810ed9c1>] each_symbol_section+0x121/0x130
[    9.759417]  [<ffffffff810eda01>] find_symbol+0x31/0x70
[    9.759420]  [<ffffffff810ef5bf>] load_module+0x20f/0x2660
[    9.759422]  [<ffffffff8104ef10>] ? __do_page_fault+0x190/0x4e0
[    9.759426]  [<ffffffff815880ec>] ? retint_restore_args+0x13/0x13
[    9.759427]  [<ffffffff815880ec>] ? retint_restore_args+0x13/0x13
[    9.759433]  [<ffffffff810ae73d>] ? trace_hardirqs_on_caller+0x11d/0x1e0
[    9.759437]  [<ffffffff812fcc0e>] ? trace_hardirqs_on_thunk+0x3a/0x3f
[    9.759439]  [<ffffffff815880ec>] ? retint_restore_args+0x13/0x13
[    9.759441]  [<ffffffff810f1ade>] SyS_init_module+0xce/0x100
[    9.759443]  [<ffffffff81587429>] system_call_fastpath+0x12/0x17
[    9.759445] ---[ end trace 9294429076a9c644 ]---

As per the comment this site should be fine, but lets wrap it in
preempt_disable() anyhow to placate lockdep.

Cc: Rusty Russell <rusty@rustcorp.com.au>
Acked-by: Paul E. McKenney <paulmck@linux.vnet.ibm.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

kernel/module.c

@@ -1169,11 +1169,17 @@ static inline int check_modstruct_version(Elf_Shdr *sechdrs,
 {
 	const unsigned long *crc;
 
-	/* Since this should be found in kernel (which can't be removed),
-	 * no locking is necessary. */
+	/*
+	 * Since this should be found in kernel (which can't be removed), no
+	 * locking is necessary -- use preempt_disable() to placate lockdep.
+	 */
+	preempt_disable();
 	if (!find_symbol(VMLINUX_SYMBOL_STR(module_layout), NULL,
-			 &crc, true, false))
+			 &crc, true, false)) {
+		preempt_enable();
 		BUG();
+	}
+	preempt_enable();
 	return check_version(sechdrs, versindex,
 			     VMLINUX_SYMBOL_STR(module_layout), mod, crc,
 			     NULL);