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 test, but may cause __my_cpu_offset
to return garbage value before it is initialized in cpu_init() called
by setup_arch, so accessing a percpu variable before setup_arch may cause
kernel hang. But the generic__my_cpu_offset always returns zero before
percpu area is brought up.
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.
Cc: Tejun Heo <t...@kernel.org>
Cc: Peter Zijlstra <pet...@infradead.org>
Cc: Ingo Molnar <mi...@redhat.com>
Cc: Rob Herring <rob.herr...@calxeda.com>
Cc: Will Deacon <will.dea...@arm.com>
Cc: Nicolas Pitre <n...@linaro.org>
Cc: Russell King <rmk+ker...@arm.linux.org.uk>
Signed-off-by: Ming Lei <tom.leim...@gmail.com>
---
arch/arm/kernel/setup.c | 7 +++++++
1 file changed, 7 insertions(+)
diff --git a/arch/arm/kernel/setup.c b/arch/arm/kernel/setup.c
index 3f6cbb2..bc7ee4b 100644
--- a/arch/arm/kernel/setup.c
+++ b/arch/arm/kernel/setup.c
@@ -439,6 +439,13 @@ void __init smp_setup_processor_id(void)
for (i = 1; i < nr_cpu_ids; ++i)
cpu_logical_map(i) = i == cpu ? 0 : i;
+ /*
+ * clear __my_cpu_offset on boot CPU early to avoid hang
+ * caused by accessing percpu variable before percpu area is
+ * brought up
+ */
+ set_my_cpu_offset(0);
+
printk(KERN_INFO "Booting Linux on physical CPU 0x%x\n", mpidr);
}
--
1.7.9.5
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