[027/114] x86, hotplug: Serialize CPU hotplug to avoid bringup concurrency issues

[Greg KH]

2.6.35-stable review patch.  If anyone has any objections, please let us know.

------------------

From: Borislav Petkov <bp@xxxxxxxxx>

commit d7c53c9e822a4fefa13a0cae76f3190bfd0d5c11 upstream.

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 ]

Signed-off-by: Borislav Petkov <borislav.petkov@xxxxxxx>
LKML-Reference: <20100819181029.GC17171@aftab>
Signed-off-by: H. Peter Anvin <hpa@xxxxxxxxxxxxxxx>
Signed-off-by: Greg Kroah-Hartman <gregkh@xxxxxxx>

---
 arch/x86/Kconfig          |    5 +++++
 arch/x86/kernel/smpboot.c |   19 +++++++++++++++++++
 2 files changed, 24 insertions(+)

--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -247,6 +247,11 @@ 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"
 
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -91,6 +91,25 @@ 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)])


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