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Subject[tip:x86/asm] x86/asm/entry/64: Simplify looping around preempt_schedule_irq()
Commit-ID:  36acef2510853e2831047ca9e22d333ba7a1047b
Gitweb: http://git.kernel.org/tip/36acef2510853e2831047ca9e22d333ba7a1047b
Author: Denys Vlasenko <dvlasenk@redhat.com>
AuthorDate: Tue, 31 Mar 2015 19:00:07 +0200
Committer: Ingo Molnar <mingo@kernel.org>
CommitDate: Wed, 1 Apr 2015 13:17:39 +0200

x86/asm/entry/64: Simplify looping around preempt_schedule_irq()

At the 'exit_intr' label we test whether interrupt/exception was in
kernel. If it did, we jump to the 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 the test succeeded last
time, preemption doesn't change the fact that interrupt/exception
was in the kernel.

We can go back directly to checking PER_CPU_VAR(__preempt_count) instead.

This makes the 'exit_intr' label unused, drop it.

Signed-off-by: Denys Vlasenko <dvlasenk@redhat.com>
Cc: Alexei Starovoitov <ast@plumgrid.com>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Frederic Weisbecker <fweisbec@gmail.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Steven Rostedt <rostedt@goodmis.org>
Cc: Will Drewry <wad@chromium.org>
Link: http://lkml.kernel.org/r/1427821211-25099-5-git-send-email-dvlasenk@redhat.com
Signed-off-by: Ingo Molnar <mingo@kernel.org>
---
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 9f8d01f..bad285d 100644
--- a/arch/x86/kernel/entry_64.S
+++ b/arch/x86/kernel/entry_64.S
@@ -654,7 +654,6 @@ 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 */
@@ -741,12 +740,12 @@ 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
/*

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