2013/1/15 Colin Cross <ccr...@android.com>: > On Mon, Jan 14, 2013 at 4:25 PM, Frederic Weisbecker <fweis...@gmail.com> > wrote: >> 2013/1/15 Colin Cross <ccr...@android.com>: >>> On Mon, Jan 14, 2013 at 4:13 PM, Frederic Weisbecker <fweis...@gmail.com> >>> wrote: >>>> I believe this is pretty much what the RCU stall detector does >>>> already: checks for other CPUs being responsive. The only difference >>>> is on how it checks that. For RCU it's about checking for CPUs >>>> reporting quiescent states when requested to do so. In your case it's >>>> about ensuring the hrtimer interrupt is well handled. >>>> >>>> One thing you can do is to enqueue an RCU callback (cal_rcu()) every >>>> minute so you can force other CPUs to report quiescent states >>>> periodically and thus check for lockups. >>> >>> That's a good point, I'll take a look at using that. A minute is too >>> long, some SoCs have maximum HW watchdog periods of under 30 seconds, >>> but a call_rcu every 10-20 seconds might be sufficient. >> >> Sure. And you can tune CONFIG_RCU_CPU_STALL_TIMEOUT accordingly. > > After considering this, I think the hrtimer watchdog is more useful. > RCU stalls are not usually panic events, and I wouldn't want to add a > panic on every RCU stall. The lack of stack traces on the affected > cpu makes a panic important. I'm planning to add an ARM DBGPCSR panic > handler, which will be able to dump the PC of a stuck cpu even if it > is not responding to interrupts. kexec or kgdb on panic might also > allow some inspection of the stack on stuck cpu. > > Failing to process interrupts is a much more serious event than an RCU > stall, and being able to detect them separately may be very valuable > for debugging.
RCU stalls can happen for different reasons: softlockup (failure to schedule another task), hardlockup (failure to process interrupts), or a bug in RCU itself. But if you have a hardlockup, it will report it. Now why do you need a panic in any case? I don't know DBGPCSR, is this a breakpoint register? How do you plan to use it remotely from the CPU that detects the lockup? -- 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/