On Tue, Jun 2, 2015 at 3:43 AM, Jiri Kosina <jkos...@suse.cz> wrote: > On Tue, 2 Jun 2015, Jiri Bohac wrote: > >> > Looking over the leapsecond code, I noticed the printk messages >> > reporting the leapsecond insertion in the second_overflow path >> > were not using the printk_deferred method. This was surprising >> > since the printk_deferred method was added in part to avoid >> > printk-ing while holding the timekeeping locks. >> > >> > See 6d9bcb621b0b (timekeeping: use printk_deferred when holding >> > timekeeping seqlock) for further rational. >> > >> > I can only guess that this omission was a git add -p oversight. >> >> second_overflow() is called from accumulate_nsecs_to_secs(). >> >> accumulate_nsecs_to_secs() is called from update_wall_time() >> - once directly >> - once via logarithmic_accumulation() >> Both calls are before write_seqcount_begin(&tk_core.seq). >> >> So it looks safe to use printk there. > > Couldn't we stuff a couple of > > !lockdep_is_held() > > assertions into printk() so that we don't have to keep rediscovering this > sort of problems over and over again?
Yea. I was thinking if we could add something very early in printk before we disable lockdep where we lockdep_aquire/release a few of the locks we know printk might take, it would help close the gap on these sorts of call paths that surprise us. Lockdep is *such* a great tool, because it provides some confidence that changes don't cause locking regressions, so to have printk poke a hole in that confidence is frustrating. thanks -john -- 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/
