x86/entry/traps: Don't force in_interrupt() to return true in IST handlers

Forcing in_interrupt() to return true if we're not in a bona fide
interrupt confuses the softirq code.  This fixes warnings like:

  NOHZ: local_softirq_pending 282

... which can happen when running things like selftests/x86.

This will change perf's static percpu buffer usage in IST context.
I think this is okay, and it's changing the behavior to match
historical (pre-4.0) behavior.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Andy Lutomirski <luto@amacapital.net>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Oleg Nesterov <oleg@redhat.com>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Cc: stable@vger.kernel.org
Fixes: 959274753857 ("x86, traps: Track entry into and exit from IST context")
Link: http://lkml.kernel.org/r/cdc215f94d118d691d73df35275022331156fb45.1464130360.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index d159048..00f03d8 100644 (file)
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -96,6 +96,12 @@ static inline void cond_local_irq_disable(struct pt_regs *regs)
                local_irq_disable();
 }
 
+/*
+ * In IST context, we explicitly disable preemption.  This serves two
+ * purposes: it makes it much less likely that we would accidentally
+ * schedule in IST context and it will force a warning if we somehow
+ * manage to schedule by accident.
+ */
 void ist_enter(struct pt_regs *regs)
 {
        if (user_mode(regs)) {
@@ -110,13 +116,7 @@ void ist_enter(struct pt_regs *regs)
                rcu_nmi_enter();
        }
 
-       /*
-        * We are atomic because we're on the IST stack; or we're on
-        * x86_32, in which case we still shouldn't schedule; or we're
-        * on x86_64 and entered from user mode, in which case we're
-        * still atomic unless ist_begin_non_atomic is called.
-        */
-       preempt_count_add(HARDIRQ_OFFSET);
+       preempt_disable();
 
        /* This code is a bit fragile.  Test it. */
        RCU_LOCKDEP_WARN(!rcu_is_watching(), "ist_enter didn't work");
@@ -124,7 +124,7 @@ void ist_enter(struct pt_regs *regs)
 
 void ist_exit(struct pt_regs *regs)
 {
-       preempt_count_sub(HARDIRQ_OFFSET);
+       preempt_enable_no_resched();
 
        if (!user_mode(regs))
                rcu_nmi_exit();
@@ -155,7 +155,7 @@ void ist_begin_non_atomic(struct pt_regs *regs)
        BUG_ON((unsigned long)(current_top_of_stack() -
                               current_stack_pointer()) >= THREAD_SIZE);
 
-       preempt_count_sub(HARDIRQ_OFFSET);
+       preempt_enable_no_resched();
 }
 
 /**
@@ -165,7 +165,7 @@ void ist_begin_non_atomic(struct pt_regs *regs)
  */
 void ist_end_non_atomic(void)
 {
-       preempt_count_add(HARDIRQ_OFFSET);
+       preempt_disable();
 }
 
 static nokprobe_inline int