On Thu, 13 Mar 2014 16:58:38 +0100 Jan Kara <j...@suse.cz> wrote: > When there are lots of messages accumulated in printk buffer, printing > them (especially over serial console) can take a long time (tens of > seconds). stop_machine() will effectively make all cpus spin in > multi_cpu_stop() waiting for the CPU doing printing to print all the > messages which triggers NMI softlockup watchdog and RCU stall detector > which add even more to the messages to print. Since machine doesn't do > anything (except serving interrupts) during this time, also network > connections are dropped and other disturbances may happen. > > Paper over the problem by waiting for printk buffer to be empty before > starting to stop CPUs. In theory a burst of new messages can be appended > to the printk buffer before CPUs enter multi_cpu_stop() so this isn't a 100% > solution but it works OK in practice and I'm not aware of a reasonably > simple better solution. >
Yes it's rather hacky, but it's simple and direct and explicit and obvious. It's the stealth hackiness which causes harm. -- 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/
