Hello, Linus, Andrew. On Wed, Jan 10, 2018 at 05:29:00PM +0100, Petr Mladek wrote: > Where is the acceptable compromise? I am not sure. So far, the most > forceful people (Linus) did not see softlockups as a big problem. > They rather wanted to see the messages. Can you please chime in? Would you be opposed to offloading to an independent context even if it were only for cases where we were already punting? The thing with the current offloading is that we don't know who we're offloading to. It might end up in faster or slower context, or more importantly a dangerous one. The particular case that we've been seeing regularly in the fleet was the following scenario. 1. Console is IPMI emulated serial console. Super slow. Also netconsole is in use. 2. System runs out of memory, OOM triggers. 3. OOM handler is printing out OOM debug info. 4. While trying to emit the messages for netconsole, the network stack / driver tries to allocate memory and then fail, which in turn triggers allocation failure or other warning messages. printk was already flushing, so the messages are queued on the ring. 5. OOM handler keeps flushing but 4 repeats and the queue is never shrinking. Because OOM handler is trapped in printk flushing, it never manages to free memory and no one else can enter OOM path either, so the system is trapped in this state. The system usually never recovers in time once this sort of condition hits and the following was the patch that I suggested which only punts when messages are already being punted and we can easily make it less punty by delaying the punting by N messages. http://lkml.kernel.org/r/20171102135258.GO3252168@xxxxxxxxxxxxxxxxxxxxxxxxxxx We definitely can fix the above described case by e.g. preventing printk flushing task from queueing more messages or whatever, but it just seems really dumb for the system to die from things like this in general and it doesn't really take all that much to trigger the condition. Thanks. -- tejun -- To unsubscribe, send a message with 'unsubscribe linux-mm' in the body to majordomo@xxxxxxxxx. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: <a href=mailto:"dont@xxxxxxxxx";> email@xxxxxxxxx </a>
