Re: BUG on 3.0-rc on commitd72bce0e67e8afc6eb959f656013cbb577426f1e

[Steven Rostedt]

On Mon, 2011-06-13 at 10:06 -0500, Andrew Theurer wrote:
> On Fri, 2011-06-10 at 18:27 +0200, Peter Zijlstra wrote:
> > On Fri, 2011-06-10 at 10:34 -0500, Andrew Theurer wrote:
> > > RIP: 0010:[<ffffffff8104e8c1>]  [<ffffffff8104e8c1>] find_lowest_rq+0xa1/0x150
> > 
> > If you've still got the vmlinux around, could you find out where in
> > find_lowest_rq that RIP is? 
> 
> Does this help?

I take it back, it looks like this does help.

> 
> 
> from objdump -d -S
> 
> ffffffff8104e820 <find_lowest_rq>:
> ffffffff8104e820:       55                      push   %rbp
> ffffffff8104e821:       48 89 e5                mov    %rsp,%rbp
> ffffffff8104e824:       48 83 ec 30             sub    $0x30,%rsp
> ffffffff8104e828:       48 89 5d d8             mov    %rbx,-0x28(%rbp)
> ffffffff8104e82c:       4c 89 65 e0             mov    %r12,-0x20(%rbp)
> ffffffff8104e830:       4c 89 6d e8             mov    %r13,-0x18(%rbp)
> ffffffff8104e834:       4c 89 75 f0             mov    %r14,-0x10(%rbp)
> ffffffff8104e838:       4c 89 7d f8             mov    %r15,-0x8(%rbp)
> ffffffff8104e83c:       e8 3f bf 48 00          callq  ffffffff814da780 <mcount>
> ffffffff8104e841:       48 c7 c0 88 e8 00 00    mov    $0xe888,%rax
> ffffffff8104e848:       65 48 03 04 25 50 dc    add    %gs:0xdc50,%rax
> ffffffff8104e84f:       00 00
> ffffffff8104e851:       65 44 8b 2c 25 58 dc    mov    %gs:0xdc58,%r13d
> ffffffff8104e858:       00 00
> ffffffff8104e85a:       83 bf bc 01 00 00 01    cmpl   $0x1,0x1bc(%rdi)
> ffffffff8104e861:       4c 8b 20                mov    (%rax),%r12
> ffffffff8104e864:       48 8b 47 08             mov    0x8(%rdi),%rax
> ffffffff8104e868:       8b 58 18                mov    0x18(%rax),%ebx
> ffffffff8104e86b:       75 23                   jne    ffffffff8104e890 <find_lowest_rq+0x70>
> ffffffff8104e86d:       b8 ff ff ff ff          mov    $0xffffffff,%eax
> ffffffff8104e872:       48 8b 5d d8             mov    -0x28(%rbp),%rbx
> ffffffff8104e876:       4c 8b 65 e0             mov    -0x20(%rbp),%r12
> ffffffff8104e87a:       4c 8b 6d e8             mov    -0x18(%rbp),%r13
> ffffffff8104e87e:       4c 8b 75 f0             mov    -0x10(%rbp),%r14
> ffffffff8104e882:       4c 8b 7d f8             mov    -0x8(%rbp),%r15
> ffffffff8104e886:       c9                      leaveq
> ffffffff8104e887:       c3                      retq
> ffffffff8104e888:       0f 1f 84 00 00 00 00    nopl   0x0(%rax,%rax,1)
> ffffffff8104e88f:       00
> ffffffff8104e890:       89 d8                   mov    %ebx,%eax
> ffffffff8104e892:       49 c7 c7 c0 2a 01 00    mov    $0x12ac0,%r15
> ffffffff8104e899:       48 89 fe                mov    %rdi,%rsi
> ffffffff8104e89c:       48 8b 04 c5 40 a3 bf    mov    -0x7e405cc0(,%rax,8),%rax
> ffffffff8104e8a3:       81
> ffffffff8104e8a4:       4c 89 e2                mov    %r12,%rdx
> ffffffff8104e8a7:       49 8b 84 07 88 08 00    mov    0x888(%r15,%rax,1),%rax
> ffffffff8104e8ae:       00
> ffffffff8104e8af:       48 83 c0 38             add    $0x38,%rax
> ffffffff8104e8b3:       48 89 c7                mov    %rax,%rdi
> ffffffff8104e8b6:       e8 85 75 0a 00          callq  ffffffff810f5e40 <cpupri_find>
> ffffffff8104e8bb:       85 c0                   test   %eax,%eax
> ffffffff8104e8bd:       74 ae                   je     ffffffff8104e86d <find_lowest_rq+0x4d>
> ffffffff8104e8bf:       89 d8                   mov    %ebx,%eax
> ffffffff8104e8c1:       41 0f a3 1c 24          bt     %ebx,(%r12)

Following the asm here, I figured we are here:

static int find_lowest_rq(struct task_struct *task)
{
	struct sched_domain *sd;
	struct cpumask *lowest_mask = __get_cpu_var(local_cpu_mask);
	int this_cpu = smp_processor_id();
	int cpu      = task_cpu(task);

	if (task->rt.nr_cpus_allowed == 1)
		return -1; /* No other targets possible */

	if (!cpupri_find(&task_rq(task)->rd->cpupri, task, lowest_mask))
		return -1; /* No targets found */

	/*
	 * At this point we have built a mask of cpus representing the
	 * lowest priority tasks in the system.  Now we want to elect
	 * the best one based on our affinity and topology.
	 *
	 * We prioritize the last cpu that the task executed on since
	 * it is most likely cache-hot in that location.
	 */
	if (cpumask_test_cpu(cpu, lowest_mask))  <<<----------- HERE
		return cpu;


Looks to me that lowest_mask is NULL???

Does this happen on boot up? Hmm, could be, by looking at Peter's patch,
he could be waking them up and we are getting into this code before
lowest_mask is defined.

Could you try this patch?

-- Steve

diff --git a/kernel/sched_rt.c b/kernel/sched_rt.c
index 88725c9..46e3e09 100644
--- a/kernel/sched_rt.c
+++ b/kernel/sched_rt.c
@@ -1239,6 +1239,10 @@ static int find_lowest_rq(struct task_struct *task)
 	int this_cpu = smp_processor_id();
 	int cpu      = task_cpu(task);
 
+	/* Make sure everything is initialized first */
+	if (system_state != SYSTEM_RUNNING)
+		return -1;
+
 	if (task->rt.nr_cpus_allowed == 1)
 		return -1; /* No other targets possible */
 


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