From 0996e0f38540beb13688e70b4b6f22e07aab2458 Mon Sep 17 00:00:00 2001
From: Andrew Cooper <andrew.cooper3@citrix.com>
Date: Thu, 11 Feb 2016 16:48:38 +0100
Subject: [PATCH] x86/traps: prevent interleaving of concurrent cpu state dumps

If two cpus enter show_execution_state() concurrently, the resulting console
output interleaved, and of no help debugging the situation further.

As calls to these locations are rare and usually important, it is acceptable
to serialise them.  These codepaths are also on the terminal error paths, so
the console lock must be the lock used for serialisation, to allow
console_force_unlock() to function properly.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Acked-by: Jan Beulich <jbeulich@suse.com>
---
 xen/arch/x86/traps.c       | 12 ++++++++++++
 xen/drivers/char/console.c | 16 ++++++++++++++++
 xen/include/xen/console.h  |  2 ++
 3 files changed, 30 insertions(+)

diff --git a/xen/arch/x86/traps.c b/xen/arch/x86/traps.c
index d19250a907..ab7deee678 100644
--- a/xen/arch/x86/traps.c
+++ b/xen/arch/x86/traps.c
@@ -416,12 +416,19 @@ void show_stack_overflow(unsigned int cpu, const struct cpu_user_regs *regs)
 
 void show_execution_state(const struct cpu_user_regs *regs)
 {
+    /* Prevent interleaving of output. */
+    unsigned long flags = console_lock_recursive_irqsave();
+
     show_registers(regs);
     show_stack(regs);
+
+    console_unlock_recursive_irqrestore(flags);
 }
 
 void vcpu_show_execution_state(struct vcpu *v)
 {
+    unsigned long flags;
+
     printk("*** Dumping Dom%d vcpu#%d state: ***\n",
            v->domain->domain_id, v->vcpu_id);
 
@@ -433,10 +440,15 @@ void vcpu_show_execution_state(struct vcpu *v)
 
     vcpu_pause(v); /* acceptably dangerous */
 
+    /* Prevent interleaving of output. */
+    flags = console_lock_recursive_irqsave();
+
     vcpu_show_registers(v);
     if ( guest_kernel_mode(v, &v->arch.user_regs) )
         show_guest_stack(v, &v->arch.user_regs);
 
+    console_unlock_recursive_irqrestore(flags);
+
     vcpu_unpause(v);
 }
 
diff --git a/xen/drivers/char/console.c b/xen/drivers/char/console.c
index e0083f1cd4..f4f61412d4 100644
--- a/xen/drivers/char/console.c
+++ b/xen/drivers/char/console.c
@@ -865,6 +865,22 @@ void console_end_log_everything(void)
     atomic_dec(&print_everything);
 }
 
+unsigned long console_lock_recursive_irqsave(void)
+{
+    unsigned long flags;
+
+    local_irq_save(flags);
+    spin_lock_recursive(&console_lock);
+
+    return flags;
+}
+
+void console_unlock_recursive_irqrestore(unsigned long flags)
+{
+    spin_unlock_recursive(&console_lock);
+    local_irq_restore(flags);
+}
+
 void console_force_unlock(void)
 {
     watchdog_disable();
diff --git a/xen/include/xen/console.h b/xen/include/xen/console.h
index c7fd9ca8ea..ea06fd8078 100644
--- a/xen/include/xen/console.h
+++ b/xen/include/xen/console.h
@@ -21,6 +21,8 @@ int console_has(const char *device);
 
 int fill_console_start_info(struct dom0_vga_console_info *);
 
+unsigned long console_lock_recursive_irqsave(void);
+void console_unlock_recursive_irqrestore(unsigned long flags);
 void console_force_unlock(void);
 
 void console_start_sync(void);
-- 
2.30.2