ARM: 7669/1: keep __my_cpu_offset consistent with generic one
Commit 14318efb(ARM: 7587/1: implement optimized percpu variable access)
introduces arm's __my_cpu_offset to optimize percpu vaiable access,
which really works well on hackbench, but will cause __my_cpu_offset
to return garbage value before it is initialized in cpu_init() called
by setup_arch, so accessing percpu variable before setup_arch may cause
kernel hang. But generic __my_cpu_offset always returns zero before
percpu area is brought up, and won't hang kernel.
So the patch tries to clear __my_cpu_offset on boot CPU early
to avoid boot hang.
At least now percpu variable is accessed by lockdep before
setup_arch(), and enabling CONFIG_LOCK_STAT or CONFIG_DEBUG_LOCKDEP
can trigger kernel hang.
Signed-off-by: Ming Lei <tom.leiming@gmail.com>
Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 1522c7a..dd1c6aa 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -456,6 +456,13 @@
for (i = 1; i < nr_cpu_ids; ++i)
cpu_logical_map(i) = i == cpu ? 0 : i;
+ /*
+ * clear __my_cpu_offset on boot CPU to avoid hang caused by
+ * using percpu variable early, for example, lockdep will
+ * access percpu variable inside lock_release
+ */
+ set_my_cpu_offset(0);
+
printk(KERN_INFO "Booting Linux on physical CPU 0x%x\n", mpidr);
}
