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

Denys Vlasenko
2015-03-31T10:33:41Z

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