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Don't disable preemption in exception handlers without IST

PATCH Applied Andi Kleen 2 participants 2 messages Oct 27, 2007

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Andi Kleen

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#0 lore raw

PATCH 1/1 Don't disable preemption in exception handlers without IST

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 <[email protected]>
arch/x86_64/kernel/traps.c +13 -11
Index: linux-2.6.23-rt1/arch/x86_64/kernel/traps.c
===================================================================
@@ -81,20 +81,22 @@ static inline void conditional_sti(struc
 		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)
 {
-	preempt_disable();
+	if (stack)
+		preempt_disable();
 	if (regs->eflags & X86_EFLAGS_IF)
 		local_irq_enable();
 }
 
-static inline void preempt_conditional_cli(struct pt_regs *regs)
+static inline void preempt_conditional_cli(struct pt_regs *regs, int stack)
 {
 	if (regs->eflags & X86_EFLAGS_IF)
 		local_irq_disable();
 	/* Make sure to not schedule here because we could be running
 	   on an exception stack. */
-	preempt_enable_no_resched();
+	if (stack)
+		preempt_enable_no_resched();
 }
 
 int kstack_depth_to_print = 12;

@@ -663,9 +665,9 @@ asmlinkage void do_stack_segment(struct 
 	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);
 }
 
 asmlinkage void do_double_fault(struct pt_regs * regs, long error_code)

@@ -821,9 +823,9 @@ asmlinkage void __kprobes do_int3(struct
 	if (notify_die(DIE_INT3, "int3", regs, error_code, 3, SIGTRAP) == NOTIFY_STOP) {
 		return;
 	}
-	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);
 }
 
 /* Help handler running on IST stack to switch back to user stack

@@ -861,7 +863,7 @@ asmlinkage void __kprobes do_debug(struc
 						SIGTRAP) == NOTIFY_STOP)
 		return;
 
-	preempt_conditional_sti(regs);
+	preempt_conditional_sti(regs, DEBUG_STACK);
 
 	/* Mask out spurious debug traps due to lazy DR7 setting */
 	if (condition & (DR_TRAP0|DR_TRAP1|DR_TRAP2|DR_TRAP3)) {

@@ -906,13 +908,13 @@ asmlinkage void __kprobes do_debug(struc
 
 clear_dr7:
 	set_debugreg(0UL, 7);
-	preempt_conditional_cli(regs);
+	preempt_conditional_cli(regs, DEBUG_STACK);
 	return;
 
 clear_TF_reenable:
 	set_tsk_thread_flag(tsk, TIF_SINGLESTEP);
 	regs->eflags &= ~TF_MASK;
-	preempt_conditional_cli(regs);
+	preempt_conditional_cli(regs, DEBUG_STACK);
 }
 
 static int kernel_math_error(struct pt_regs *regs, const char *str, int trapnr)
Applied
#1 lore raw

--

Quoted 6 lines · Andi Kleen

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.

Quoted 6 lines

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 <[email protected]>

Thanks, applied.

-- Steve