From: Borislav Petkov <bp@amd64.org>
Date: Thu, 19 Aug 2010 18:10:29 +0000 (+0200)
Subject: x86, hotplug: Serialize CPU hotplug to avoid bringup concurrency issues
X-Git-Tag: v2.6.36-rc2~11^2~1
X-Git-Url: http://bbs.cooldavid.org/git/?a=commitdiff_plain;ds=sidebyside;h=d7c53c9e822a4fefa13a0cae76f3190bfd0d5c11;p=net-next-2.6.git

x86, hotplug: Serialize CPU hotplug to avoid bringup concurrency issues

When testing cpu hotplug code on 32-bit we kept hitting the "CPU%d:
Stuck ??" message due to multiple cores concurrently accessing the
cpu_callin_mask, among others.

Since these codepaths are not protected from concurrent access due to
the fact that there's no sane reason for making an already complex
code unnecessarily more complex - we hit the issue only when insanely
switching cores off- and online - serialize hotplugging cores on the
sysfs level and be done with it.

[ v2.1: fix !HOTPLUG_CPU build ]

Cc: <stable@kernel.org>
Signed-off-by: Borislav Petkov <borislav.petkov@amd.com>
LKML-Reference: <20100819181029.GC17171@aftab>
Signed-off-by: H. Peter Anvin <hpa@linux.intel.com>
---

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index a84fc34c8f7..ac7827fc082 100644
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -245,6 +245,11 @@ config ARCH_HWEIGHT_CFLAGS
 
 config KTIME_SCALAR
 	def_bool X86_32
+
+config ARCH_CPU_PROBE_RELEASE
+	def_bool y
+	depends on HOTPLUG_CPU
+
 source "init/Kconfig"
 source "kernel/Kconfig.freezer"
 
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index abf4a86ffc5..8b3bfc4dd70 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -90,6 +90,25 @@ DEFINE_PER_CPU(int, cpu_state) = { 0 };
 static DEFINE_PER_CPU(struct task_struct *, idle_thread_array);
 #define get_idle_for_cpu(x)      (per_cpu(idle_thread_array, x))
 #define set_idle_for_cpu(x, p)   (per_cpu(idle_thread_array, x) = (p))
+
+/*
+ * We need this for trampoline_base protection from concurrent accesses when
+ * off- and onlining cores wildly.
+ */
+static DEFINE_MUTEX(x86_cpu_hotplug_driver_mutex);
+
+void cpu_hotplug_driver_lock()
+{
+        mutex_lock(&x86_cpu_hotplug_driver_mutex);
+}
+
+void cpu_hotplug_driver_unlock()
+{
+        mutex_unlock(&x86_cpu_hotplug_driver_mutex);
+}
+
+ssize_t arch_cpu_probe(const char *buf, size_t count) { return -1; }
+ssize_t arch_cpu_release(const char *buf, size_t count) { return -1; }
 #else
 static struct task_struct *idle_thread_array[NR_CPUS] __cpuinitdata ;
 #define get_idle_for_cpu(x)      (idle_thread_array[(x)])