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Patch "x86/entry/traps: Don't force in_interrupt() to return true in IST handlers" has been added to the 4.4-stable tree

PATCH [email protected] 1 participant 1 message Jun 18, 2016

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This is a note to let you know that I've just added the patch titled

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

to the 4.4-stable tree which can be found at:
http://www.kernel.org/git/?p=linux/kernel/git/stable/stable-queue.git;a=summary

The filename of the patch is:
x86-entry-traps-don-t-force-in_interrupt-to-return-true-in-ist-handlers.patch
and it can be found in the queue-4.4 subdirectory.

If you, or anyone else, feels it should not be added to the stable tree, please let <[email protected]> know about it.

Quoted 1 line

From aaee8c3c5cce2d9107310dd9f3026b4f901d441c Mon Sep 17 00:00:00 2001

From: Andy Lutomirski <[email protected]>
Date: Tue, 24 May 2016 15:54:04 -0700
Subject: x86/entry/traps: Don't force in_interrupt() to return true in IST handlers

From: Andy Lutomirski <[email protected]>

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 <[email protected]>
Cc Andy Lutomirski <[email protected]>
Cc Borislav Petkov <[email protected]>
Cc Brian Gerst <[email protected]>
Cc Denys Vlasenko <[email protected]>
Cc H. Peter Anvin <[email protected]>
Cc Linus Torvalds <[email protected]>
Cc Oleg Nesterov <[email protected]>
Cc Peter Zijlstra <[email protected]>
Cc Thomas Gleixner <[email protected]>
Fixes 959274753857 ("x86, traps: Track entry into and exit from IST context")
Link http://lkml.kernel.org/r/cdc215f94d118d691d73df35275022331156fb45.1464130360.git.luto@kernel.org open here
Signed-off-by Ingo Molnar <[email protected]>
Signed-off-by Greg Kroah-Hartman <[email protected]>
---
 arch/x86/kernel/traps.c |   20 ++++++++++----------
 1 file changed, 10 insertions(+), 10 deletions(-)
arch/x86/kernel/traps.c +10 -10
@@ -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

Patches currently in stable-queue which might be from [email protected] are

queue-4.4/x86-entry-traps-don-t-force-in_interrupt-to-return-true-in-ist-handlers.patch