queue/x86-dumpstack-Pin-the-target-stack-when-dumping-it.patch

From 8a567429ebb70da56eb63f05deee51d9328c5c00 Mon Sep 17 00:00:00 2001
From: Andy Lutomirski <luto@kernel.org>
Date: Thu, 15 Sep 2016 22:45:45 -0700
Subject: [PATCH] x86/dumpstack: Pin the target stack when dumping it

commit 1959a60182f48879635812a03a99c02231ea8677 upstream.

Specifically, pin the stack in save_stack_trace_tsk() and
show_trace_log_lvl().

This will prevent a crash if the target task dies before or while
dumping its stack once we start freeing task stacks early.

Signed-off-by: Andy Lutomirski <luto@kernel.org>
Cc: Borislav Petkov <bp@alien8.de>
Cc: Brian Gerst <brgerst@gmail.com>
Cc: Denys Vlasenko <dvlasenk@redhat.com>
Cc: H. Peter Anvin <hpa@zytor.com>
Cc: Jann Horn <jann@thejh.net>
Cc: Josh Poimboeuf <jpoimboe@redhat.com>
Cc: Linus Torvalds <torvalds@linux-foundation.org>
Cc: Peter Zijlstra <peterz@infradead.org>
Cc: Thomas Gleixner <tglx@linutronix.de>
Link: http://lkml.kernel.org/r/cf0082cde65d1941a996d026f2b2cdbfaca17bfa.1474003868.git.luto@kernel.org
Signed-off-by: Ingo Molnar <mingo@kernel.org>

diff --git a/arch/x86/kernel/dumpstack_32.c b/arch/x86/kernel/dumpstack_32.c
index 09675712eba8..8ad32dc94e8d 100644
--- a/arch/x86/kernel/dumpstack_32.c
+++ b/arch/x86/kernel/dumpstack_32.c
@@ -95,6 +95,9 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	unsigned long *stack;
 	int i;
 
+	if (!try_get_task_stack(task))
+		return;
+
 	if (sp == NULL) {
 		if (regs)
 			sp = (unsigned long *)regs->sp;
@@ -118,6 +121,8 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	}
 	pr_cont("\n");
 	show_trace_log_lvl(task, regs, sp, bp, log_lvl);
+
+	put_task_stack(task);
 }
 
 
diff --git a/arch/x86/kernel/dumpstack_64.c b/arch/x86/kernel/dumpstack_64.c
index 9ee4520ce83c..1bcdb164afd9 100644
--- a/arch/x86/kernel/dumpstack_64.c
+++ b/arch/x86/kernel/dumpstack_64.c
@@ -253,6 +253,9 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 	int cpu;
 	int i;
 
+	if (!try_get_task_stack(task))
+		return;
+
 	preempt_disable();
 	cpu = smp_processor_id();
 
@@ -303,6 +306,8 @@ show_stack_log_lvl(struct task_struct *task, struct pt_regs *regs,
 
 	pr_cont("\n");
 	show_trace_log_lvl(task, regs, sp, bp, log_lvl);
+
+	put_task_stack(task);
 }
 
 void show_regs(struct pt_regs *regs)
diff --git a/arch/x86/kernel/stacktrace.c b/arch/x86/kernel/stacktrace.c
index 4738f5e0f2ab..b3f32fbe3ba4 100644
--- a/arch/x86/kernel/stacktrace.c
+++ b/arch/x86/kernel/stacktrace.c
@@ -79,9 +79,14 @@ void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 
 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 {
+	if (!try_get_task_stack(tsk))
+		return;
+
 	dump_trace(tsk, NULL, NULL, 0, &save_stack_ops_nosched, trace);
 	if (trace->nr_entries < trace->max_entries)
 		trace->entries[trace->nr_entries++] = ULONG_MAX;
+
+	put_task_stack(tsk);
 }
 EXPORT_SYMBOL_GPL(save_stack_trace_tsk);
 
-- 
2.15.0