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    SubjectRe: [PATCH] tracing/core: Add current context on tracing recursion warning

    * Frederic Weisbecker <fweisbec@gmail.com> wrote:

    > On Sun, Apr 19, 2009 at 02:34:32PM +0200, Frederic Weisbecker wrote:
    > > On Sun, Apr 19, 2009 at 02:14:54PM +0800, Li Zefan wrote:
    > > > Frederic Weisbecker wrote:
    > > > > Hi,
    > > > >
    > > > > Here is the v3 of the __string() field patchset.
    > > > > It applies suggestions from Steven and Peter with some arrangements.
    > > > >
    > > > > This time, filtering is not supported (though it is ready in a pending patch).
    > > > > I wanted to provide it but it looks like filtering has been broken recently.
    > > > > Once I set a usual string filter, no more traces appear, and clearing it
    > > > > doesn't change anything.
    > > > >
    > > >
    > > > I tried it, and triggered a WARNING, and ring buffers was
    > > > disabled permanently:
    > >
    > >
    > > I've also seen this warning but on another event.
    > > I don't think this is related to this patchset but
    > > more about the tracing recursion detection.
    > >
    > > For exemple, here we are in an Irq event, which doesn't
    > > use the __string() thing. For such off-case, the only change
    > > is a variable declaration and a + 0 operation.
    > >
    > > Another thing: I've only seen it in a selftest.
    >
    >
    > Worst: I can't reproduce it anymore.
    > What were you doing when you got such warning? Were you
    > in a selftest, or trying a usual event?
    >
    > Also, could you test the following patch. It will give us
    > more informations about the tracing recursion.
    >
    > You can find it on:
    >
    > git://git.kernel.org/pub/scm/linux/kernel/git/frederic/random-tracing tracing/recursion
    >
    > It's against tip/tracing/core
    >
    > Thanks!
    >
    > ---
    > >From d13bf59ca011b976c561f623e3189a4a5b94370e Mon Sep 17 00:00:00 2001
    > From: Frederic Weisbecker <fweisbec@gmail.com>
    > Date: Sun, 19 Apr 2009 15:30:19 +0200
    > Subject: [PATCH] tracing/core: Add current context on tracing recursion warning

    >
    > In case of tracing recursion detection, we only get the stacktrace.
    > But the current context may be very useful to debug the issue.
    >
    > This patch adds the softirq/hardirq/nmi context with the warning
    > using lockdep context display to have a familiar output.
    >
    > [ Impact: more information in tracing recursion ]
    >
    > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com>
    > ---
    > kernel/trace/ring_buffer.c | 13 +++++++++++++
    > 1 files changed, 13 insertions(+), 0 deletions(-)
    >
    > diff --git a/kernel/trace/ring_buffer.c b/kernel/trace/ring_buffer.c
    > index b421b0e..27a6e7d 100644
    > --- a/kernel/trace/ring_buffer.c
    > +++ b/kernel/trace/ring_buffer.c
    > @@ -1493,8 +1493,21 @@ static int trace_recursive_lock(void)
    > level = trace_irq_level();
    >
    > if (unlikely(current->trace_recursion & (1 << level))) {
    > + static atomic_t warned;
    > +
    > /* Disable all tracing before we do anything else */
    > tracing_off_permanent();
    > +
    > + if (atomic_inc_return(&warned) == 1) {
    > + printk(KERN_WARNING "Tracing recursion: "
    > + "[HC%u[%lu]:SC%u[%lu]:NMI[%lu]:HE%u:SE%u]\n",
    > + current->hardirq_context,
    > + hardirq_count() >> HARDIRQ_SHIFT,
    > + current->softirq_context,
    > + softirq_count() >> SOFTIRQ_SHIFT,
    > + in_nmi(), current->hardirqs_enabled,
    > + current->softirqs_enabled);
    > + }

    It would be nice to have this ... but there's no need to do that
    atomic thing - just use printk_once() please. (if we race with
    another instance and get two messages that's not a problem)

    Ingo


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