On Fri, 8 Nov 2013 11:21:13 +0100 Jan Kara <j...@suse.cz> wrote: > On Fri 08-11-13 00:46:49, Frederic Weisbecker wrote: > > On Thu, Nov 07, 2013 at 06:37:17PM -0500, Steven Rostedt wrote: > > > On Fri, 8 Nov 2013 00:21:51 +0100 > > > Frederic Weisbecker <fweis...@gmail.com> wrote: > > > > > > > > Offloading to a workqueue would be perhaps better, and writing to the > > > > serial > > > > console could then be done with interrupts enabled, preemptible > > > > context, etc... > > > > > > Oh God no ;-) Adding workqueue logic into printk just spells a > > > nightmare of much more complexity for a critical kernel infrastructure. > > > > But yeah that's scary, that means workqueues itself can't printk that > > safely. > > So, you're right after all. > Yeah, we've been there (that was actually my initial proposal). But > Andrew and Steven (rightfully) objected and suggested irq_work should be > used instead.
I still hate the patchset and so does everyone else, including you ;) There must be something smarter we can do. Let's start by restating the problem: CPU A is in printk, emitting log_buf characters to a slow device. Meanwhile other CPUs come into printk(), see that the system is busy, dump their load into log_buf then scram, leaving CPU A to do even more work. Correct so far? If so, what is the role of local_irq_disabled() in this? Did CPU A call printk() with local interrupts disabled, or is printk (or the console driver) causing the irqs-off condition? Where and why is this IRQ disablement happening? Could we fix this problem by not permitting CPUs B, C and D to DoS CPU A? When CPU B comes into printk() and sees that printk is busy, make CPU A hand over to CPU B and let CPU A get out of there? -- 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/
