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>

diff --git a/arch/x86/kernel/entry_64.S b/arch/x86/kernel/entry_64.S
index 9f8d01f1f1b2fae67ff9e14d118052e46a1bd169..bad285d84a9fc65f8edb4d36fbfe9f43a02600a5 100644 (file)
--- 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
        /*