Red Hat Bugzilla – Bug 113182
smp kernel hangs on dual processor system when fast printks are done
Last modified: 2007-11-30 17:07:00 EST
From Bugzilla Helper: User-Agent: Mozilla/5.0 (X11; U; Linux i686; en-US; rv:1.0.2) Gecko/20030208 Netscape/7.02 Description of problem: I have a set of related questions 1. My machine is dual processor dell Machine. /proc/cpuinfo shows 2 processors. So my understanding of smp kernel says that linux should allow 2 kernel threads to run. So even if one gets caught into infinite loop, scheduler shpuld be able to schedule other processes on the other processor. But it doesn't seem to happen if I write a simple module in the module_init function of which I add a simple infinite loop. while (1). The machine gets hung. Even though it seems to accepts interrupts generated by NIC i.e. even though I can ping to the machine, I cant login neither can I any input from keyboard is accepted at the console. So should be other processes scheduled on other processor ? 2. Now, assuming that only one kernel thread can execute if I do current=jiffies while (jiffies - current < 100) printk(" ###############"); then again there occurs a hang for some time 100 millseconds and then the messages sudfdenly come, And if I gve very large difference while (jiffies - current < 10000) printk(" ###############"); the machine gets hung permanently. It even doesnt show any message. Now I added a delay of 200 ms before printk just to check avoid some stress on printk and even then I faced same problem. I think I am doing / assuming something very wrong Can someone explain this phenomenon to me ? Thanks Anand Version-Release number of selected component (if applicable): 2.4.21-4.ELsmp How reproducible: Always Steps to Reproduce: 1. write simplest module 2.and add the code I have mentioned above for verious problems in module_init. 3.load the module Actual Results: system hung Expected Results: no hang and messages on console Additional info:
Hi I see it's you again ;) Your code is buggy.
I am really sorry if I am missing something. The problem I had mentioned earlier was different. This problem is might be a narrowed version of earlier problem. The code is actually onlye 10 lines. 1. For the first case in which I put kernel thread in infinite loop on a multiprocessor machine the code is module_init() { int i,j,k; while (1); return 0; } 2. For second case it is extern unsigned int jiffies; module_init() { int i,j,k; unsigned int current=jiffies; while (jiffies - current < 10000) printk(" ###############"); return 0; } Please let me know what is the bug in this code.