On 04/23/2014 05:37 PM, Jiri Kosina wrote: > On Wed, 23 Apr 2014, Rik van Riel wrote: > >> Echoing values into /proc/sysrq-trigger seems to be a popular way to >> get information out of the kernel. However, dumping information about >> thousands of processes, or hundreds of CPUs to serial console can >> result in IRQs being blocked for minutes, resulting in various kinds >> of cascade failures. >> >> The most common failure is due to interrupts being blocked for a very >> long time. This can lead to things like failed IO requests, and other >> things the system cannot easily recover from. >> >> This problem is easily fixable by making __handle_sysrq use RCU >> instead of spin_lock_irqsave. >> >> This leaves the warning that RCU grace periods have not elapsed for a >> long time, but the system will come back from that automatically. > > This, however, will make RCU stall detector to send NMI to all online CPUs > so that they can dump their stacks.
It already does that, since several of the longer-running sysrq handlers already grab rcu_read_lock(), for example show_state(). > IOW, this might actually make the whole sysrq dump last for much longer, > and have the log polluted with all-CPU dumps for no good reason. > > I wonder whether explicitly setting rcu_cpu_stall_suppress during sysrq > handling might be a viable workaround for this. I suppose that would do the trick. -- All rights reversed -- 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/
