[PATCH 5/5 v2] x86/asm/entry/64: simplify looping around preempt_schedule_irq

[Denys Vlasenko <dvlasenk@redhat.com>]

At this label, we test whether interrupt/exception was in kernel.
If it did, we jump to preemption check. If preemption does happen
(IOW if we call preempt_schedule_irq), we go back to exit_intr.

But it's pointless, we already know that test succeeded last time,
preemption doesn't change the fact that interrupt/exception
was in kernel. We can go back directly to checking
PER_CPU_VAR(__preempt_count) instead.

This makes exit_intr label unused. Dropping it.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
CC: Linus Torvalds <torvalds@linux-foundation.org>
CC: Steven Rostedt <rostedt@goodmis.org>
CC: Ingo Molnar <mingo@kernel.org>
CC: Borislav Petkov <bp@alien8.de>
CC: "H. Peter Anvin" <hpa@zytor.com>
CC: Andy Lutomirski <luto@amacapital.net>
CC: Oleg Nesterov <oleg@redhat.com>
CC: Frederic Weisbecker <fweisbec@gmail.com>
CC: Alexei Starovoitov <ast@plumgrid.com>
CC: Will Drewry <wad@chromium.org>
CC: Kees Cook <keescook@chromium.org>
CC: x86@kernel.org
CC: linux-kernel@vger.kernel.org
---

Changes in v2:
* split insn cleanups into a separate patch
* improve commit log message

 arch/x86/kernel/entry_64.S | 7 +++----
 1 file changed, 3 insertions(+), 4 deletions(-)

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 16bf357..356266c 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -653,7 +653,6 @@ ret_from_intr:
 	CFI_DEF_CFA_REGISTER	rsp
 	CFI_ADJUST_CFA_OFFSET	RBP
 
-exit_intr:
 	testl $3,CS(%rsp)
 	je retint_kernel
 	/* Interrupt came from user space */
@@ -740,12 +739,12 @@ retint_kernel:
 #ifdef CONFIG_PREEMPT
 	/* Interrupts are off */
 	/* Check if we need preemption */
-	cmpl	$0,PER_CPU_VAR(__preempt_count)
-	jnz	1f
 	bt	$9,EFLAGS(%rsp)	/* interrupts were off? */
 	jnc	1f
+0:	cmpl	$0,PER_CPU_VAR(__preempt_count)
+	jnz	1f
 	call	preempt_schedule_irq
-	jmp	exit_intr
+	jmp	0b
 1:
 #endif
 	/*
-- 
1.8.1.4