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    SubjectRe: [PATCH 0/5] [GIT PULL] updates for tip/tracing/ftrace


    On Sat, 21 Mar 2009, Frederic Weisbecker wrote:

    > On Sat, Mar 21, 2009 at 01:44:07PM -0400, Steven Rostedt wrote:
    > >
    > > On Sat, 21 Mar 2009, Frederic Weisbecker wrote:
    > > > > Testing tracer sched_switch: PASSED
    > > > > initcall init_sched_switch_trace+0x0/0x12 returned 0 after 99609 usecs
    > > > > calling init_stack_trace+0x0/0x12 @ 1
    > > > > Testing tracer sysprof: .. no entries found ..FAILED!
    > > > > initcall init_stack_trace+0x0/0x12 returned -1 after 101562 usecs
    > > > > initcall init_stack_trace+0x0/0x12 returned with error code -1
    > > > > calling init_function_trace+0x0/0x12 @ 1
    > > > > Testing tracer function: PASSED
    > > > > initcall init_function_trace+0x0/0x12 returned 0 after 104492 usecs
    > > > > calling init_irqsoff_tracer+0x0/0x2c @ 1
    > > > > Testing tracer irqsoff: .. no entries found ..FAILED!
    > > > > Testing tracer preemptoff: .. no entries found ..FAILED!
    > > > > Testing tracer preemptirqsoff: .. no entries found ..FAILED!
    > > >
    > > >
    > > > It's strange that the {*}_off tracers have failed.
    > >
    > > Does this have your changes in it? The ones that solved this before.
    >
    >
    > You mean Lai's patch for RCU?
    > I haven't seen such tracers failures since it has been merged.
    > I don't think it's related.

    No, I mean your patches for the selftest (tracing_stop).

    >
    >
    > > >
    > > >
    > > > > initcall init_irqsoff_tracer+0x0/0x2c returned 0 after 8789 usecs
    > > > > calling init_wakeup_tracer+0x0/0x58 @ 1
    > > > > Testing tracer wakeup: .. no entries found ..FAILED!
    > > >
    > > >
    > > > This one too. (sysprof doesn't count, it fails for some weeks, I think
    > > > it's not a hard deal to fix).
    > > >
    > > >
    > > > > initcall init_wakeup_tracer+0x0/0x58 returned -1 after 298828 usecs
    > > > > initcall init_wakeup_tracer+0x0/0x58 returned with error code -1
    > > > > calling stack_trace_init+0x0/0xc7 @ 1
    > > > > initcall stack_trace_init+0x0/0xc7 returned 0 after 0 usecs
    > > > > calling init_mmio_trace+0x0/0x12 @ 1
    > > > > initcall init_mmio_trace+0x0/0x12 returned 0 after 0 usecs
    > > > > calling init_graph_trace+0x0/0x12 @ 1
    > > > > Testing tracer function_graph: <3>INFO: RCU detected CPU 0 stall (t=4294678940/10000 jiffies)
    > > > > Pid: 1, comm: swapper Not tainted 2.6.29-rc8-tip-02752-g47b1aea-dirty #3264
    > > > > Call Trace:
    > > > > <IRQ> [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff80211150>] print_context_stack+0xa0/0xd3
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff8020fb26>] dump_trace+0x22d/0x2cc
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff80211008>] show_trace_log_lvl+0x51/0x5d
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff80211029>] show_trace+0x15/0x17
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff802111fa>] dump_stack+0x77/0x81
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff8029e6dd>] print_cpu_stall+0x40/0xa4
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff8029e8be>] check_cpu_stall+0x49/0x76
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff8029e902>] __rcu_pending+0x17/0xfc
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff8029ea13>] rcu_pending+0x2c/0x5e
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff8026abef>] update_process_times+0x3c/0x77
    > > > > [<ffffffff8020c79d>] return_to_handler+0x0/0x73
    > > > > [<ffffffff802875dd>] tick_periodic+0x6e/0x70
    > > >
    > > >
    > > > Still hanging in the timer interrupt.
    > > > I guess it makes the timer interrupt servicing too slow and then
    > > > once it is serviced, another one is raised.
    > > >
    > > > But the cause is perhaps more complex
    > > >
    > > > I think you have had too much hanging of this type.
    > > > I'm preparing a fix that checks periodically if the function graph
    > > > tracer is spending too much time in an interrupt.
    > > >
    > > > I guess I could count the number of function executed between the irq entry
    > > > and its exit.
    > > >
    > > > That's the best: if we are hanging in an interrupt, it could be whatever
    > > > interrupt and the jiffies could not be progressing so I can't rely
    > > > on time but only on number of functions executed.
    > > >
    > > > May be 10000 calls is a good threshold before killing the function graph
    > > > inside an interrupt?
    > > >
    > > > Let's try, I will also provide a way to dump the function graph traces from
    > > > the ring-buffer on the screen, it could help to debug it in this case.
    > >
    > > I was thinking the same thing. All you need to do is add a "ftrace_dump()"
    > > in the print_cpu_stall() function in kernel/rcuclassic.c.
    >
    >
    > Perhaps not relying on rcu cpu ctall detector, because it could perhaps
    > hang without it.
    > I think I should directly call ftrace_dump() from the tracer and not
    > rely on CONFIG that might not be enabled.

    Have we seen the hang without it?

    And where would you call ftrace_dump? Note, once ftrace_dump is called,
    tracing is permantently disabled.

    -- Steve

    >
    >
    > > You would need to add "#include <linux/ftrace.h>" too.
    > >
    > > /me wonders if we should add ftrace_dump() to kernel.h to remove that
    > > requirement?
    > >
    > > -- Steve
    > >
    >
    >


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