* Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > On Mon, 2011-06-06 at 17:52 +0200, Ingo Molnar wrote: > > * Peter Zijlstra <peterz@xxxxxxxxxxxxx> wrote: > > > > > Needs more staring at, preferably by someone who actually > > > understands that horrid mess :/ Also, this all still doesn't make > > > printk() work reliably while holding rq->lock. > > > > So, what about my suggestion to just *remove* the wakeup from there > > and use the deferred wakeup mechanism that klogd uses. > > > > That would make printk() *visibly* more robust in practice. > > That's currently done from the jiffy tick, do you want to effectively > delay releasing the console_sem for the better part of a jiffy? Yes, and we already do it in some other circumstances. Can you see any problem with that? klogd is an utter slowpath anyway. > > [ It would also open up the way to possibly make printk() NMI entry > > safe - currently we lock up if we printk in an NMI or #MC context > > that happens to nest inside a printk(). ] > > Well, for that to happen you also need to deal with logbuf_lock > nesting. [...] That we could do as a robustness patch: detect when the current CPU already holds it and do not lock up on that. This would also allow printk() to work within a crashing printk(). (assuming the second printk() does not crash - in which case it's game over anyway) > Personally I think using printk() from NMI context is quite beyond > sane. Yeah, quite so, but it *can* happen so if we can make it work as a free side-effect of a printk()-robustness increasing patch, why not? Thanks, Ingo -- To unsubscribe from this list: send the line "unsubscribe linux-tip-commits" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
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