From: Steven Rostedt <rostedt@goodmis.org>
To: Fengguang Wu <fengguang.wu@intel.com>
Cc: LKML <linux-kernel@vger.kernel.org>,
"Paul E. McKenney" <paulmck@us.ibm.com>
Subject: Re: lockdep WARNING on check_critical_timing()
Date: Thu, 06 Sep 2012 17:00:29 -0400 [thread overview]
Message-ID: <1346965229.1680.48.camel@gandalf.local.home> (raw)
In-Reply-To: <20120905015937.GA20175@localhost>
On Wed, 2012-09-05 at 09:59 +0800, Fengguang Wu wrote:
> Greetings,
>
> This is possibly an aged warning.
>
> if (!hardirq_count()) {
> if (softirq_count()) {
> /* like the above, but with softirqs */
> => DEBUG_LOCKS_WARN_ON(current->softirqs_enabled);
>
> [ 3.600059] Testing tracer preemptoff:
> [ 3.760076] ------------[ cut here ]------------
> [ 3.760866] WARNING: at /c/kernel-tests/src/stable/kernel/lockdep.c:3506 check_flags+0x125/0x154()
> [ 3.762160] Modules linked in:
> [ 3.762643] Pid: 1, comm: swapper/0 Not tainted 3.6.0-rc3-00013-g01f8a27 #158
> [ 3.763679] Call Trace:
> [ 3.764053] [<c1020916>] warn_slowpath_common+0x4d/0x62
> [ 3.764838] [<c105c000>] ? check_flags+0x125/0x154
> [ 3.765567] [<c102093f>] warn_slowpath_null+0x14/0x18
> [ 3.766317] [<c105c000>] check_flags+0x125/0x154
> [ 3.766998] [<c105e02f>] lock_acquire+0x3b/0xef
> [ 3.767689] [<c12461ba>] _raw_spin_lock_irqsave+0x3e/0x4e
> [ 3.768494] [<c12404b8>] ? check_critical_timing+0x112/0x160
> [ 3.769340] [<c12404b8>] check_critical_timing+0x112/0x160
> [ 3.770047] [<c1027474>] ? __do_softirq+0x19b/0x1f9
> [ 3.770047] [<c1027474>] ? __do_softirq+0x19b/0x1f9
> [ 3.770047] [<c1088549>] trace_preempt_on+0x8d/0xc9
> [ 3.770047] [<c1027238>] ? __local_bh_enable+0x87/0x8a
> [ 3.770047] [<c1046c85>] sub_preempt_count+0x7f/0x9c
> [ 3.770047] [<c1027238>] __local_bh_enable+0x87/0x8a
> [ 3.770047] [<c1027474>] __do_softirq+0x19b/0x1f9
> [ 3.770047] [<c10272d9>] ? ftrace_define_fields_irq_handler_entry+0x45/0x45
> [ 3.770047] <IRQ> [<c1027723>] ? irq_exit+0x4f/0xa9
> [ 3.770047] [<c1015e03>] ? smp_apic_timer_interrupt+0x70/0x7e
> [ 3.770047] [<c1246daf>] ? apic_timer_interrupt+0x2f/0x34
> [ 3.770047] [<c108007b>] ? ring_buffer_discard_commit+0x24c/0x24c
> [ 3.770047] [<c1139c87>] ? __const_udelay+0x1/0x1c
> [ 3.770047] [<c108566f>] ? trace_selftest_startup_preemptoff+0x74/0xed
> [ 3.770047] [<c1085b57>] ? register_tracer+0x11c/0x1f7
> [ 3.770047] [<c13c1bf3>] ? init_function_trace+0xf/0xf
> [ 3.770047] [<c13c1c00>] ? init_irqsoff_tracer+0xd/0x11
> [ 3.770047] [<c1001158>] ? do_one_initcall+0x70/0x118
> [ 3.770047] [<c13afa03>] ? kernel_init+0xec/0x169
> [ 3.770047] [<c13af917>] ? start_kernel+0x2f2/0x2f2
> [ 3.770047] [<c124773a>] ? kernel_thread_helper+0x6/0x10
>
This is the same as a previous bug. It is caused by rcu doing the check
in the function tracer and then triggering a lockdep warning.
Paul,
Didn't we talk about having the rcu_dereference_raw() not do the check?
The function tracer is just too invasive to add work arounds to prevent
lockdep from screaming about it.
-- Steve
next prev parent reply other threads:[~2012-09-06 21:00 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
2012-09-05 1:59 lockdep WARNING on check_critical_timing() Fengguang Wu
2012-09-06 21:00 ` Steven Rostedt [this message]
2012-09-06 21:29 ` Paul E. McKenney
2012-09-06 21:56 ` Steven Rostedt
2012-09-06 22:08 ` Paul E. McKenney
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