Messages in this thread | | | Date | Mon, 19 Jan 2009 14:04:42 +0100 | From | Ingo Molnar <> | Subject | Re: [PATCH] ftrace based hard lockup detector |
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* Steven Rostedt <rostedt@goodmis.org> wrote:
> On Sun, 18 Jan 2009, Frederic Weisbecker wrote: > > > Like the NMI watchdog, this feature try to detect hard lockups by > > lurking at the non-progress of the timer interrupts. > > > > You can enable it at boot time by passing the ftrace_hardlockup parameter. > > I plan to add a debugfs file to enable/disable at runtime. > > > > When a hardlockup is detected, it will print a backtrace. Perhaps it > > would be good to print the locks held from lockdep too? > > > > It only support x86 for the moment, because a kind of generic timer interrupt > > counter is needed on all archs to have it generic. > > > > Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> > > Hi Frederic, > > This seems like a rewrite of the NMI lockup code. In my debugging, I > simply put ftrace_dump in the NMI lockup, which gives me a ftrace dump > as soon as NMI detects a lockup. I'm a bit confused at what this gives > us over that?
this is different from the NMI watchdog in a number of ways:
- it works on all platforms and in all situations where the NMI watchdog does not work.
- in theory it can detect hard lockups in situations where the NMI watchdog is disabled, such as suspend/resume or early bootup. (especially early bootup lockups are nasty and the NMI watchdog is enabled relatively late)
- it could be extended to detect 'soft' lockups too - i.e. we could have a one-stop facility to detect all kinds of "kernel does not seem to progress" lockups.
But it's not as complete as the NMI watchdog: it relies on instrumented function calls rolling on and on during the lockup - that's not the case when we get a hard lockup due to a tight, infinite loop somewhere.
Ingo
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