[PATCH-RT] Fix for sleeping function called from invalid context when running gdb

[John Kacur <jkacur@redhat.com>]

While running gdb on cyclictest on v3.2-rc2-rt3 I got the following error

[root@starship ~]# [11887.443716] BUG: sleeping function called from invalid con
text at /home/jkacur/linux-rt/kernel/rtmutex.c:645
[11887.443720] in_atomic(): 1, irqs_disabled(): 0, pid: 4859, name: cyclictest
[11887.443723] no locks held by cyclictest/4859.
[11887.443726] Pid: 4859, comm: cyclictest Not tainted 3.2.0-rc2-rt3-debug-expr+
 #1
[11887.443728] Call Trace:
[11887.443737]  [<ffffffff81035543>] __might_sleep+0x185/0x18d
[11887.443743]  [<ffffffff8107c3ed>] rt_spin_lock_fastlock.clone.0+0x24/0x31
[11887.443749]  [<ffffffff813fba9b>] rt_spin_lock+0x16/0x40
[11887.443754]  [<ffffffff81053eee>] force_sig_info+0x3d/0xeb
[11887.443758]  [<ffffffff81053fb2>] force_sig+0x16/0x18
[11887.443761]  [<ffffffff813fd0a1>] do_trap+0xef/0x130
[11887.443766]  [<ffffffff81076525>] ? trace_hardirqs_on_caller+0x12a/0x161
[11887.443771]  [<ffffffff813fd16f>] do_int3+0x8d/0x9a
[11887.443774]  [<ffffffff813fc9e7>] int3+0x27/0x40

I found that there is a patch for this in v2.6.33.9-rt31 that I forward-ported
to v3.2-rc2-rt3

I believe that Thomas Gleixner is the original author, but I'm not sure.
Thomas - can you provide your signed-off-by if you are the author?

Forward-ported from v2.6.33.9-rt31 to v3.2-rc2-rt3
Signed-off-by: John Kacur <jkacur@redhat.com>
---
 arch/x86/kernel/traps.c |   24 +++++++++++++-----------
 1 files changed, 13 insertions(+), 11 deletions(-)

diff --git a/arch/x86/kernel/traps.c b/arch/x86/kernel/traps.c
index a8e3eb8..3654390 100644
--- a/arch/x86/kernel/traps.c
+++ b/arch/x86/kernel/traps.c
@@ -87,9 +87,10 @@ 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();
 }
@@ -100,11 +101,12 @@ 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();
 }
 
 static void __kprobes
@@ -222,9 +224,9 @@ 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)
@@ -316,9 +318,9 @@ 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
@@ -412,12 +414,12 @@ 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,
 				error_code, 1);
-		preempt_conditional_cli(regs);
+		preempt_conditional_cli(regs, DEBUG_STACK);
 		return;
 	}
 
@@ -436,7 +438,7 @@ 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;
 }
-- 
1.7.2.3