x86/entry: Make irqs_disabled checks in exit code depend on lockdep

These checks are quite slow.  Disable them in non-lockdep
kernels to reduce the performance hit.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: linux-kernel@vger.kernel.org
Link: http://lkml.kernel.org/r/eccff2a154ae6fb50f40228901003a6e9c24f3d0.1444091585.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

arch/x86/entry/common.c

@@ -219,7 +219,7 @@ static struct thread_info *pt_regs_to_thread_info(struct pt_regs *regs)
 /* Called with IRQs disabled. */
 __visible void prepare_exit_to_usermode(struct pt_regs *regs)
 {
-	if (WARN_ON(!irqs_disabled()))
+	if (IS_ENABLED(CONFIG_PROVE_LOCKING) && WARN_ON(!irqs_disabled()))
 		local_irq_disable();
 
 	lockdep_sys_exit();
@@ -281,8 +281,8 @@ __visible void syscall_return_slowpath(struct pt_regs *regs)
 
 	CT_WARN_ON(ct_state() != CONTEXT_KERNEL);
 
-	if (WARN(irqs_disabled(), "syscall %ld left IRQs disabled",
-		 regs->orig_ax))
+	if (IS_ENABLED(CONFIG_PROVE_LOCKING) &&
+	    WARN(irqs_disabled(), "syscall %ld left IRQs disabled", regs->orig_ax))
 		local_irq_enable();
 
 	/*