[PATCH 4.4 47/75] x86/entry/traps: Dont force in_interrupt() to return true in IST handlers

Greg Kroah-Hartman
2016-06-22T23:15:51Z

From: Andy Lutomirski <luto@kernel.org>

commit aaee8c3c5cce2d9107310dd9f3026b4f901d441c upstream.

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>
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>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

---
arch/x86/kernel/traps.c | 20 ++++++++++----------
1 file changed, 10 insertions(+), 10 deletions(-)

--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -109,6 +109,12 @@ static inline void preempt_conditional_c
preempt_count_dec();
}

+/*
+ * 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)) {
@@ -123,13 +129,7 @@ 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");
@@ -137,7 +137,7 @@ 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();
@@ -168,7 +168,7 @@ void ist_begin_non_atomic(struct pt_regs
BUG_ON((unsigned long)(current_top_of_stack() -
current_stack_pointer()) >= THREAD_SIZE);

- preempt_count_sub(HARDIRQ_OFFSET);
+ preempt_enable_no_resched();
}

/**
@@ -178,7 +178,7 @@ void ist_begin_non_atomic(struct pt_regs
*/
void ist_end_non_atomic(void)
{
- preempt_count_add(HARDIRQ_OFFSET);
+ preempt_disable();
}

static nokprobe_inline int