Messages in this thread | | | Date | Mon, 24 Sep 2012 21:04:20 -0700 | From | "Paul E. McKenney" <> | Subject | Re: RCU idle CPU detection is broken in linux-next |
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On Tue, Sep 25, 2012 at 01:41:18AM +0200, Frederic Weisbecker wrote: > 2012/9/25 Frederic Weisbecker <fweisbec@gmail.com>: > > 2012/9/25 Sasha Levin <levinsasha928@gmail.com>: > >> On 09/25/2012 01:06 AM, Frederic Weisbecker wrote: > >>> 2012/9/25 Sasha Levin <levinsasha928@gmail.com>: > >>>> On 09/25/2012 12:47 AM, Sasha Levin wrote: > >>>>> - While I no longer see the warnings I've originally noticed, if I run with Paul's last debug patch I see the following warning: > >>>> > >>>> Correction: Original warnings are still there, they just got buried in the huge spew that was caused by additional debug warnings > >>>> so I've missed them initially. > >>> > >>> Are they the same? Could you send me your dmesg? > >>> > >>> Thanks. > >>> > >> > >> Log is attached, you can go directly to 168.703017 when the warnings begin. > > > > Thanks! > > > > So here is the first relevant warning: > > > > [ 168.703017] ------------[ cut here ]------------ > > [ 168.708117] WARNING: at kernel/rcutree.c:502 rcu_eqs_exit_common+0x4a/0x3a0() > > [ 168.710034] Pid: 7871, comm: trinity-child65 Tainted: G W > > 3.6.0-rc6-next-20120924-sasha-00030-g71f256c #5 > > [ 168.710034] Call Trace: > > [ 168.710034] <IRQ> [<ffffffff811c737a>] ? rcu_eqs_exit_common+0x4a/0x3a0 > > [ 168.710034] [<ffffffff811078b6>] warn_slowpath_common+0x86/0xb0 > > [ 168.710034] [<ffffffff811079a5>] warn_slowpath_null+0x15/0x20 > > [ 168.710034] [<ffffffff811c737a>] rcu_eqs_exit_common+0x4a/0x3a0 > > [ 168.710034] [<ffffffff811c79cc>] rcu_eqs_exit+0x9c/0xb0 > > [ 168.710034] [<ffffffff811c7a4c>] rcu_user_exit+0x6c/0xd0 > > [ 168.710034] [<ffffffff8106eb1f>] do_general_protection+0x1f/0x170 > > [ 168.710034] [<ffffffff83a0e624>] ? restore_args+0x30/0x30 > > [ 168.710034] [<ffffffff83a0e875>] general_protection+0x25/0x30 > > [ 168.710034] [<ffffffff810a3f06>] ? native_read_msr_safe+0x6/0x20 > > [ 168.710034] [<ffffffff81a0b34b>] __rdmsr_safe_on_cpu+0x2b/0x50 > > [ 168.710034] [<ffffffff819ec971>] ? list_del+0x11/0x40 > > [ 168.710034] [<ffffffff811886dc>] > > generic_smp_call_function_single_interrupt+0xec/0x120 > > [ 168.710034] [<ffffffff81151147>] ? account_system_vtime+0xd7/0x140 > > [ 168.710034] [<ffffffff81096f72>] > > smp_call_function_single_interrupt+0x22/0x40 > > [ 168.710034] [<ffffffff83a0fe2f>] call_function_single_interrupt+0x6f/0x80 > > [ 168.710034] <EOI> [<ffffffff83a0e5f4>] ? retint_restore_args+0x13/0x13 > > [ 168.710034] [<ffffffff811c7285>] ? rcu_user_enter+0x105/0x110 > > [ 168.710034] [<ffffffff8107e06d>] syscall_trace_leave+0xfd/0x150 > > [ 168.710034] [<ffffffff83a0f1ef>] int_check_syscall_exit_work+0x34/0x3d > > [ 168.710034] ---[ end trace fd408dd21b70b87c ]--- > > > > This is an exception inside an interrupt, and the interrupt > > interrupted RCU user mode. > > And we have that nesting: > > > > rcu_irq_enter(); <--- irq entry > > rcu_user_exit(); <--- exception entry > > > > And rcu_eqs_exit() doesn't handle that very well... > > So either I should return immediately from rcu_user_exit() if > we are in an interrupt, or we make rcu_user_exit() able to nest > on rcu_irq_enter() :)
Both of the two are eminently doable, with varying degrees of hackery.
What makes the most sense from an adaptive-idle viewpoint?
Thanx, Paul
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