x86-Don-t-disable-preemption-in-exception-handlers-w.patch

From fb8863a66463d0d1928e6115adbfbd62f5188366 Mon Sep 17 00:00:00 2001
From: Andi Kleen <ak@suse.de>
Date: Fri, 3 Jul 2009 08:44:12 -0500
Subject: [PATCH] x86: Don't disable preemption in exception handlers without IST

commit 4c67d0b3e40f01c4b681994ac64bf8f83e6caad9 in tip.

Some of the exception handlers that run on an IST in a normal kernel
still disable preemption. This causes might_sleep warning when sending signals
for debugging in PREEMPT-RT because sending signals can take a lock.
Since the ISTs are disabled now for those don't disable the preemption.

This completes the remove IST patch I sent some time ago and fixes
another case where using gdb caused warnings.

Also it will likely improve latency a little bit.

Signed-off-by: Andi Kleen <ak@suse.de>
Signed-off-by: Ingo Molnar <mingo@elte.hu>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Paul Gortmaker <paul.gortmaker@windriver.com>

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index 4cfa8fd..30ba8fd 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -88,9 +88,10 @@ static inline void conditional_sti(struct pt_regs *regs)
 		local_irq_enable();
 }
 
-static inline void preempt_conditional_sti(struct pt_regs *regs)
+static inline void preempt_conditional_sti(struct pt_regs *regs, int stack)
 {
-	inc_preempt_count();
+	if (stack)
+		inc_preempt_count();
 	if (regs->flags & X86_EFLAGS_IF)
 		local_irq_enable();
 }
@@ -101,11 +102,12 @@ static inline void conditional_cli(struct pt_regs *regs)
 		local_irq_disable();
 }
 
-static inline void preempt_conditional_cli(struct pt_regs *regs)
+static inline void preempt_conditional_cli(struct pt_regs *regs, int stack)
 {
 	if (regs->flags & X86_EFLAGS_IF)
 		local_irq_disable();
-	dec_preempt_count();
+	if (stack)
+		dec_preempt_count();
 }
 
 #ifdef CONFIG_X86_32
@@ -232,9 +234,9 @@ dotraplinkage void do_stack_segment(struct pt_regs *regs, long error_code)
 	if (notify_die(DIE_TRAP, "stack segment", regs, error_code,
 			12, SIGBUS) == NOTIFY_STOP)
 		return;
-	preempt_conditional_sti(regs);
+	preempt_conditional_sti(regs, STACKFAULT_STACK);
 	do_trap(12, SIGBUS, "stack segment", regs, error_code, NULL);
-	preempt_conditional_cli(regs);
+	preempt_conditional_cli(regs, STACKFAULT_STACK);
 }
 
 dotraplinkage void do_double_fault(struct pt_regs *regs, long error_code)
@@ -470,9 +472,9 @@ dotraplinkage void __kprobes do_int3(struct pt_regs *regs, long error_code)
 		return;
 #endif
 
-	preempt_conditional_sti(regs);
+	preempt_conditional_sti(regs, DEBUG_STACK);
 	do_trap(3, SIGTRAP, "int3", regs, error_code, NULL);
-	preempt_conditional_cli(regs);
+	preempt_conditional_cli(regs, DEBUG_STACK);
 }
 
 #ifdef CONFIG_X86_64
@@ -566,7 +568,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 		return;
 
 	/* It's safe to allow irq's after DR6 has been saved */
-	preempt_conditional_sti(regs);
+	preempt_conditional_sti(regs, DEBUG_STACK);
 
 	if (regs->flags & X86_VM_MASK) {
 		handle_vm86_trap((struct kernel_vm86_regs *) regs,
@@ -589,7 +591,7 @@ dotraplinkage void __kprobes do_debug(struct pt_regs *regs, long error_code)
 	si_code = get_si_code(tsk->thread.debugreg6);
 	if (tsk->thread.debugreg6 & (DR_STEP | DR_TRAP_BITS) || user_icebp)
 		send_sigtrap(tsk, regs, error_code, si_code);
-	preempt_conditional_cli(regs);
+	preempt_conditional_cli(regs, DEBUG_STACK);
 
 	return;
 }
-- 
1.7.1.1