On Tuesday 17 November 2015 06:14 PM, Peter Zijlstra wrote: > On Tue, Nov 17, 2015 at 06:07:08PM +0530, Vineet Gupta wrote: >> On Tuesday 17 November 2015 05:52 PM, Peter Zijlstra wrote: >>>>> BTW since we are on the topic we have this loop in stack unwinder which >>>>> can >>>>> potentially cause RCU stalls, actual lockups etc. I was planning to add >>>>> the >>>>> following - does that seem fine to you. >>> Worries me more than anything. How could you get stuck in there? >> >> No we not getting stuck in there - but this has potential to - if say unwind >> info >> were corrupt (not seen that ever though). > > Better put in a failsafe for that anyway, just out of sheer paranoia :-)
Indeed, loop for say 32 times at max or some such. > You should never report more than PERF_MAX_STACK_DEPTH thingies anyway, > so once you've done that many loops, you're good to bail, right? Yeah, although I need to ensure if arch code needs to check that. Plus the unwinder is also used for things like ps wchan, /proc/<pid>/stack, crash dump etc. >> The old code won't even respond to say a Ctrl+C if it were stuck ! >> Plus the reschedule there will keeps sched happy when say unraveling deep >> stack >> frames with perf ? > > You're likely to call this code from interrupt/NMI context, there is no > ^C or scheduling going to help you there. For perf case, but there are other uses of unwinder as described above. So in light of above, do u think that the cond_resched() + signal_pending check is not needed and the bail if over N iters will be fine ! -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
