2013/2/15 Linus Torvalds <torva...@linux-foundation.org>: > On Fri, Feb 15, 2013 at 9:44 AM, Paul E. McKenney > <paul...@linux.vnet.ibm.com> wrote: >> >> This commit was designed to increase the probability of hitting the >> races described in http://lwn.net/Articles/453002/. These races result >> in deadlocks involving the runqueue lock (and perhaps also the priority >> inheritance locks). And yes, I most certainly should have described >> this in the commit message. :-( > > Ugh. That particular race seems to be because the softirq handling is > just crazy, and does the "wakeup_softirqd()" form interrupt context, > BUT HAS SPECIFICALLY BROKEN THE IRQ COUNTING! > > Because it claims to do it from softirq context, which is pure > garbage. It's not actually in softirq context. > > The whole hardirq -> softirq transition seems stupid. I'm sure I made > some serious mistake in cleaning it up, and there's probably some > missed tracepoint (or perhaps screwed-up lockdep annotation), but I > think the hardirq -> softirq preempt thing shoudl be done as an atomic > preempt downgrade, so that we never have a window of "uhhuh, another > interrupt can come in between and see us as being in neither). And the > wakeup_softirqd should be done without playing with preempt count at > all. > > Something like this ENTIRELY UNTESTED patch. > > Note: I doubt this patch affects Dave's issue at all, I just started > looking at that do_softirq code when I read your bug explanation. > > Adding random people for kernel/softirq.c to the participants list. > Comments about the patch? Do note that it's entirely untested, so > consider it more a RFD than a real patch.. It looks like it adds a lot > of lines, but most of it is for comments and simplification of the > logic.
preempt_value_in_interrupt() looks buggy in your patch: it makes invoke_softirq() returning if (val & HARDIRQ_MASK). But that's always true since you have moved further the sub_preempt_count(IRQ_EXIT) further. -- 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/
