On Wed, Jun 18, 2014 at 04:53:14PM +0200, Jiri Kosina wrote: > On Wed, 18 Jun 2014, Paul E. McKenney wrote: > > > > > > - both RCU stall detector and 'echo l > sysrq-trigger' can (and we've > > > > > seen it happening for real) cause a complete, undebuggable, silent > > > > > hang > > > > > of machine (deadlock in NMI context) > > > > > > > > I could easily add an option to RCU to allow people to tell it not to > > > > use NMIs to dump the stack. Would that help? > > > > > > Well, that would make unfortunately the information provided by RCU stall > > > detector rather useless ... workqueue-based stack dumping is very > > > unlikely > > > to point its finger to the real offender, as it'd be coming way too late. > > > > I would not use workqueues, but rather have the CPU detecting the > > stall grovel through the other CPUs' stacks, which is what I do now for > > architectures that don't support NMI-based stack dumps. Would that be > > a reasonable approach? > > That would indeed solve lockups induced by RCU stall detector (and we > should convert sysrq stack dumping code to use the same mechanism > afterwards). > > But then, the kernel is still polluted by quite a few instances of > > WARN_ON(in_nmi()) > > BUG_IN(in_nmi()) > > if (in_nmi()) > printk(....) > > which need to be fixed separately afterwards anyway.
True enough! Thanx, Paul -- 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/