releases/4.4.14/x86-entry-traps-don-t-force-in_interrupt-to-return-true-in-ist-handlers.patch

   1 From aaee8c3c5cce2d9107310dd9f3026b4f901d441c Mon Sep 17 00:00:00 2001
   2 From: Andy Lutomirski <luto@kernel.org>
   3 Date: Tue, 24 May 2016 15:54:04 -0700
   4 Subject: x86/entry/traps: Don't force in_interrupt() to return true in IST handlers
   5
   6 From: Andy Lutomirski <luto@kernel.org>
   7
   8 commit aaee8c3c5cce2d9107310dd9f3026b4f901d441c upstream.
   9
  10 Forcing in_interrupt() to return true if we're not in a bona fide
  11 interrupt confuses the softirq code.  This fixes warnings like:
  12
  13   NOHZ: local_softirq_pending 282
  14
  15 ... which can happen when running things like selftests/x86.
  16
  17 This will change perf's static percpu buffer usage in IST context.
  18 I think this is okay, and it's changing the behavior to match
  19 historical (pre-4.0) behavior.
  20
  21 Signed-off-by: Andy Lutomirski <luto@kernel.org>
  22 Cc: Andy Lutomirski <luto@amacapital.net>
  23 Cc: Borislav Petkov <bp@alien8.de>
  24 Cc: Brian Gerst <brgerst@gmail.com>
  25 Cc: Denys Vlasenko <dvlasenk@redhat.com>
  26 Cc: H. Peter Anvin <hpa@zytor.com>
  27 Cc: Linus Torvalds <torvalds@linux-foundation.org>
  28 Cc: Oleg Nesterov <oleg@redhat.com>
  29 Cc: Peter Zijlstra <peterz@infradead.org>
  30 Cc: Thomas Gleixner <tglx@linutronix.de>
  31 Fixes: 959274753857 ("x86, traps: Track entry into and exit from IST context")
  32 Link: http://lkml.kernel.org/r/cdc215f94d118d691d73df35275022331156fb45.1464130360.git.luto@kernel.org
  33 Signed-off-by: Ingo Molnar <mingo@kernel.org>
  34 Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
  35
  36 ---
  37  arch/x86/kernel/traps.c |   20 ++++++++++----------
  38  1 file changed, 10 insertions(+), 10 deletions(-)
  39
  40 --- a/arch/x86/kernel/traps.c
  41 +++ b/arch/x86/kernel/traps.c
  42 @@ -109,6 +109,12 @@ static inline void preempt_conditional_c
  43         preempt_count_dec();
  44  }
  45
  46 +/*
  47 + * In IST context, we explicitly disable preemption.  This serves two
  48 + * purposes: it makes it much less likely that we would accidentally
  49 + * schedule in IST context and it will force a warning if we somehow
  50 + * manage to schedule by accident.
  51 + */
  52  void ist_enter(struct pt_regs *regs)
  53  {
  54         if (user_mode(regs)) {
  55 @@ -123,13 +129,7 @@ void ist_enter(struct pt_regs *regs)
  56                 rcu_nmi_enter();
  57         }
  58
  59 -       /*
  60 -        * We are atomic because we're on the IST stack; or we're on
  61 -        * x86_32, in which case we still shouldn't schedule; or we're
  62 -        * on x86_64 and entered from user mode, in which case we're
  63 -        * still atomic unless ist_begin_non_atomic is called.
  64 -        */
  65 -       preempt_count_add(HARDIRQ_OFFSET);
  66 +       preempt_disable();
  67
  68         /* This code is a bit fragile.  Test it. */
  69         RCU_LOCKDEP_WARN(!rcu_is_watching(), "ist_enter didn't work");
  70 @@ -137,7 +137,7 @@ void ist_enter(struct pt_regs *regs)
  71
  72  void ist_exit(struct pt_regs *regs)
  73  {
  74 -       preempt_count_sub(HARDIRQ_OFFSET);
  75 +       preempt_enable_no_resched();
  76
  77         if (!user_mode(regs))
  78                 rcu_nmi_exit();
  79 @@ -168,7 +168,7 @@ void ist_begin_non_atomic(struct pt_regs
  80         BUG_ON((unsigned long)(current_top_of_stack() -
  81                                current_stack_pointer()) >= THREAD_SIZE);
  82
  83 -       preempt_count_sub(HARDIRQ_OFFSET);
  84 +       preempt_enable_no_resched();
  85  }
  86
  87  /**
  88 @@ -178,7 +178,7 @@ void ist_begin_non_atomic(struct pt_regs
  89   */
  90  void ist_end_non_atomic(void)
  91  {
  92 -       preempt_count_add(HARDIRQ_OFFSET);
  93 +       preempt_disable();
  94  }
  95
  96  static nokprobe_inline int