| Message ID | 1362624468-5451-1-git-send-email-tom.leiming@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
Hello, On Thu, Mar 07, 2013 at 02:47:48AM +0000, Ming Lei wrote: > 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. For the record, can you include a backtrace or something please? The description makes it sounds like a caller bug, so it would be good to document a valid user of per-cpu before cpu_init(). Will
Hi, On Thu, Mar 7, 2013 at 11:44 AM, Will Deacon <will.deacon@arm.com> wrote: > > For the record, can you include a backtrace or something please? The lock_release_holdtime() will access percpu variable, so every lock release may trigger the hang if CONFIG_LOCK_STAT is enabled, and there are many lock acquire/release before setup_arch. No detailed backtrace since only early_printk can work at that time. > description makes it sounds like a caller bug, so it would be good to > document a valid user of per-cpu before cpu_init(). OK, I will add the document: lockdep will use percpu variable before cpu_init() called inside setup_arch(). Thanks,
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); }
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 <tj@kernel.org> 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> --- arch/arm/kernel/setup.c | 7 +++++++ 1 file changed, 7 insertions(+)