On Fri, 2007-10-05 at 18:41 +0200, Thomas Gleixner wrote: > On Fri, 5 Oct 2007, Gregory Haskins wrote: > > This series may help debugging certain circumstances where the serial > > console is unreponsive (e.g. RT51+ spinner, or scheduler problem). It changes > > the serial8250 driver to use IRQF_NODELAY so that interrupts execute in irq > > context instead of a kthread. > > > > It works pretty well on this end, though it is admitted not fully baked For > > instance, a few paths in sysrq can still call into non-raw spinlocks > > (sched_debug_show, for instance) which will cause subsequent errors. Also, > > if you use KDB, be sure to convert the kdb_printf_lock to raw as well. I may > > send a KDB related patch seperately. > > > > I am sending this out now in case it is helpful to someone. > > The simple non-patch solution is to up the priority of the serial > console irq to maximum. That's usually sufficient to catch runnaway tasks > etc. It does not interfere with the system in normal operation as long as > you do not hit keys in your minicom. > > I doubt that your patch has a chance to survive lockdep and anything which > is not a sysrq. Your point is valid, and I thought of this too. The one problem with it is that it is not immune to problems in the scheduler itself (which at the time, I thought I was chasing..turned out to be lockdep), but that is probably a rarity. In any case, we have been using it on a number of debug systems here for a few weeks and the console continues to work well in all functions besides sysrq, believe it or not (*). But I don't see this as being anything used for real. Just thought I would throw it out there in case it was useful or inspired someone to give it some love. Regards, -Greg (*) The trick is that once it figures out its not for sysrq, it schedules a (kthread based) tasklet to do the actual tty() callbacks.
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- From: Gregory Haskins <[email protected]>
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- From: Thomas Gleixner <[email protected]>
- [PATCH 0/2] [RFC] RT: Optionally allow IRQF_NODELAY on serial console
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