On Thu, May 29, 2014 at 10:09:48AM +0200, Jiri Kosina wrote: > On Thu, 29 May 2014, Frederic Weisbecker wrote: > > > > I am rather surprised that this patchset hasn't received a single review > > > comment for 3 weeks. > > > > > > Let me point out that the issues Petr is talking about in the cover > > > letter > > > are real -- we've actually seen the lockups triggered by RCU stall > > > detector trying to dump stacks on all CPUs, and hard-locking machine up > > > while doing so. > > > > > > So this really needs to be solved. > > > > The lack of review may be partly due to a not very appealing changestat > > on an old codebase that is already unpopular: > > > > Documentation/kernel-parameters.txt | 19 +- > > kernel/printk/printk.c | 1218 > > +++++++++++++++++++++++++---------- > > 2 files changed, 878 insertions(+), 359 deletions(-) > > > > > > Your patches look clean and pretty nice actually. They must be seriously > > considered if we want to keep the current locked ring buffer design and > > extend it to multiple per context buffers. But I wonder if it's worth to > > continue that way with the printk ancient design. > > > > If it takes more than 1000 line changes (including 500 added) to make it > > finally work correctly with NMIs by working around its fundamental > > flaws, shouldn't we rather redesign it to use a lockless ring buffer > > like ftrace or perf ones? > > Yeah, printk() has grown over years to a stinking pile of you-know-what, > no argument to that. > > I also agree that performing a massive rewrite, which will make it use a > lockless buffer, and therefore ultimately solve all its problems > (scheduler deadlocks, NMI deadlocks, xtime_lock deadlocks) at once, is > necessary in the long run. > > On the other hand, I am completely sure that the diffstat for such rewrite > is going to be much more scary :)
Indeed, but probably much more valuable in the long term. > > This is not adding fancy features to printk(), where we really should be > saying no; horrible commits like 7ff9554bb5 is exactly something that > should be pushed against *heavily*. But bugfixes for hard machine lockups > are a completely different story to me (until we have a whole new printk() > buffer handling implementation). Yeah bugfixes are certainly another story. Still it looks like yet another layer of workaround on a big hack. But yeah I'm certainly not in a right position to set anyone to do a massive rewrite on such a boring subsystem :) There is also a big risk that if we push back this bugfix, nobody will actually do that desired rewrite. Lets be crazy and Cc Linus on that. -- 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/
