From 81539169f283329fd8bc58457cc15754f683ba69 Mon Sep 17 00:00:00 2001
From: Josh Poimboeuf <jpoimboe@redhat.com>
Date: Fri, 16 Sep 2016 08:05:20 -0500
Subject: x86/dumpstack: Remove NULL task pointer convention

show_stack_log_lvl() and friends allow a NULL pointer for the
task_struct to indicate the current task.  This creates confusion and
can cause sneaky bugs.

Instead require the caller to pass 'current' directly.

This only changes the internal workings of the dumpstack code.  The
dump_trace() and show_stack() interfaces still allow a NULL task
pointer.  Those interfaces should also probably be fixed as well.

Signed-off-by: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/include/asm/stacktrace.h b/arch/x86/include/asm/stacktrace.h
index 780a83e..ed2be1b 100644
--- a/arch/x86/include/asm/stacktrace.h
+++ b/arch/x86/include/asm/stacktrace.h
@@ -94,7 +94,7 @@ get_frame_pointer(struct task_struct *task, struct pt_regs *regs)
 	if (regs)
 		return (unsigned long *)regs->bp;
 
-	if (!task || task == current)
+	if (task == current)
 		return __builtin_frame_address(0);
 
 	return (unsigned long *)((struct inactive_task_frame *)task->thread.sp)->bp;
@@ -113,7 +113,7 @@ get_stack_pointer(struct task_struct *task, struct pt_regs *regs)
 	if (regs)
 		return (unsigned long *)kernel_stack_pointer(regs);
 
-	if (!task || task == current)
+	if (task == current)
 		return __builtin_frame_address(0);
 
 	return (unsigned long *)task->thread.sp;
diff --git a/arch/x86/kernel/dumpstack.c b/arch/x86/kernel/dumpstack.c
index aa208e5..e0648f7 100644
--- a/arch/x86/kernel/dumpstack.c
+++ b/arch/x86/kernel/dumpstack.c
@@ -175,11 +175,13 @@ void show_stack(struct task_struct *task, unsigned long *sp)
 {
 	unsigned long bp = 0;
 
+	task = task ? : current;
+
 	/*
 	 * Stack frames below this one aren't interesting.  Don't show them
 	 * if we're printing for %current.
 	 */
-	if (!sp && (!task || task == current)) {
+	if (!sp && task == current) {
 		sp = get_stack_pointer(current, NULL);
 		bp = (unsigned long)get_frame_pointer(current, NULL);
 	}
diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 122f37d7..4ff0008 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -205,7 +205,7 @@ void show_regs(struct pt_regs *regs)
 		u8 *ip;
 
 		pr_emerg("Stack:\n");
-		show_stack_log_lvl(NULL, regs, NULL, 0, KERN_EMERG);
+		show_stack_log_lvl(current, regs, NULL, 0, KERN_EMERG);
 
 		pr_emerg("Code:");
 
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 16c0d5f..008a298 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -278,7 +278,7 @@ void show_regs(struct pt_regs *regs)
 		u8 *ip;
 
 		printk(KERN_DEFAULT "Stack:\n");
-		show_stack_log_lvl(NULL, regs, NULL, 0, KERN_DEFAULT);
+		show_stack_log_lvl(current, regs, NULL, 0, KERN_DEFAULT);
 
 		printk(KERN_DEFAULT "Code: ");
 
-- 
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