On Tue, Nov 17, 2015 at 07:02:00PM +0530, Vineet Gupta wrote: > > 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.
Ah, ok. On x86 we have a separate unwinder for perf. Trying to touch userspace memory from NMI context is a tad tricky. (imagine the NMI interrupting a page-fault and then itself triggering a page-fault again) > > 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 ! It can't hurt, but you want to engineer it to be robust for the most constrained environment, so I would say the bail over N iters had better be robust, otherwise you're screwed anyhow ;-) -- 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/
