Messages in this thread Patch in this message | | | From | Ming Lei <> | Subject | [PATCH v1] ARM: keep __my_cpu_offset consistent with generic one | Date | Thu, 7 Mar 2013 21:35:56 +0800 |
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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.
Cc: Peter Zijlstra <peterz@infradead.org> Cc: Ingo Molnar <mingo@redhat.com> Cc: Rob Herring <rob.herring@calxeda.com> Cc: Will Deacon <will.deacon@arm.com> Cc: Nicolas Pitre <nico@linaro.org> Cc: Russell King <rmk+kernel@arm.linux.org.uk> Signed-off-by: Ming Lei <tom.leiming@gmail.com> --- V1: - documents lockdep uses percpu variable early
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..1a9dc21 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 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); } -- 1.7.9.5
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