(2013/12/07 4:07), Frank Ch. Eigler wrote: > Hi, Masami - > > masami.hiramatsu.pt wrote: > >> [...] >>>> [...] Then, I'd like to propose this new whitelist feature in >>>> kprobe-tracer (not raw kprobe itself). And a sysctl knob for >>>> disabling the whitelist. That knob will be >>>> /proc/sys/debug/kprobe-event-whitelist and disabling it will mark >>>> kernel tainted so that we can check it from bug reports. >>> >>> How would one assemble a reliable whitelist, if we haven't fully >>> characterized the problems that make the blacklist necessary? >> >> As I said, we can use function graph tracer's list as the whitelist, >> since it doesn't include any functions invoked from ftrace's event >> handler. (Note that I don't mention the Systemtap or other user here) >> >> Whitelist is just for keeping the people away from the quantitative >> issue, who just want to trace their subsystems except for ftrace. >> [...] > > Would you plan to limit kprobes (or just the perf-probe frontend) to > only function-entries also?
Exactly, yes :). Currently I have a patch for kprobe-tracer implementation (not only for perf-probe, but doesn't limit kprobes itself). > If not, and if intra-function > statement-granularity kprobes remain allowed within a > function-granularity whitelist, then you might still have those > "quantitative" problems. Yes, but as far as I've tested, the performance overhead is not high, especially as far as putting kprobes at the entry of those functions because of ftrace-based optimization. > Even worse, kprobes robustness problems can bite even with a small > whitelist, unless you can test the countless subset selections > cartesian-product the aggrevating factors (like other tracing > facilities being in use at the same time, limited memory, high irq > rates, debugging sessions, architectures, whatever). And also, what script will run on each probe, right? :) >> [...] For the long term solution, I think we can introduce some >> kind of performance gatekeeper as systemtap does. Counting the >> miss-hit rate per second and if it go over a threshold, disable next >> miss-hit (or most miss-hit) probe (as OOM killer does). > > That would make sense, but again it would not help deal with kprobes > robustness (in the kernel-crashing rather than kernel-slowdown sense). Why would you think so? Is there any hidden path for calling kprobes mechanism?? The kernel crash problem just comes from bugs, not the quantitative issue. Thank you, -- Masami HIRAMATSU IT Management Research Dept. Linux Technology Center Hitachi, Ltd., Yokohama Research Laboratory E-mail: masami.hiramatsu...@hitachi.com -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
