From mboxrd@z Thu Jan 1 00:00:00 1970 From: tom.leiming@gmail.com (Ming Lei) Date: Thu, 7 Mar 2013 21:35:56 +0800 Subject: [PATCH v1] ARM: keep __my_cpu_offset consistent with generic one Message-ID: <1362663356-21151-1-git-send-email-tom.leiming@gmail.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org 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 Cc: Ingo Molnar Cc: Rob Herring Cc: Will Deacon Cc: Nicolas Pitre Cc: Russell King Signed-off-by: Ming Lei --- 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