----- Forwarded Message ----- From: "Dave Anderson" <anderson@xxxxxxxxxx> ----- "Michael Holzheu" <holzheu@xxxxxxxxxxxxxxxxxx> wrote: > On Wed, 2010-02-10 at 10:08 -0500, Dave Anderson wrote: > > ----- "Michael Holzheu" <holzheu@xxxxxxxxxxxxxxxxxx> wrote: > > > > > Hi again, > > > > > > When I change get_smp_cpus() to return "get_highest_cpu_online() + 1" I > > > > see five swapper idle tasks when using "ps". The problem I now have is > > > > that I have to provide a backtrace for the offline cpus. But the offline > > > > CPUs do not have any stack on s390. Is there a way to tell crash that > > > > there is no backtrace available? Probably I overlooked something... > > > > > > Ok, I think I got it now. In case of an offline CPU, I will use > > > "task_struct_thread_ksp" like I do it for non active tasks. > > > > > > When I do that I get for the swapper tasks with the offline CPUs: > > > > > > PID: 0 TASK: 18d38340 CPU: 2 COMMAND: "swapper" > > > #0 [18d3feb8] ret_from_fork at 117e12 > > > > > > PID: 0 TASK: 18d40440 CPU: 3 COMMAND: "swapper" > > > #0 [18d47eb8] ret_from_fork at 117e12 > > > > I'm not why you should do anything. The cpu is offline and for all > > practical purposes it doesn't exist, so why bother? > > Because you can do a "bt" on the swapper task with the offline CPU. > Then s390x_get_stack_frame() is called where I figure out the stack > pointer and instruction address. In that function I check if the task is > currently running on a CPU and in that case I get the information from > the associated s390 lowcore, where the registers are stored in case of a > dump. If the task is not running I get the information from the thread > struct. > > > The patch I have queued just uses get_highest_cpu_online()+1 and > > does nothing else. But I only tested it on a live system, and > > any backtrace attempt on the offlined swapper task just shows > > (active). What happens when you do a "bt -a" with a dumpfile? > > It shows all swapper tasks (online and offline), but I get errors for > the backtrace for the offline CPUs. What kind of errors? > > The attached patch would solve the problem (and eliminate most of the > probably redundant s390(x)_has_cpu() function. I don't see what's being solved by the patch (not the s390x_get_smp_cpus parts) -- does the "old" s390x_has_cpu() fail? Even though the task is offline, the runqueue will still show its percpu swapper task as the current task on that cpu. Dave > > With this patch "ps" shows: > > PID PPID CPU TASK ST %MEM VSZ RSS COMM > > 0 0 0 800ef0 RU 0.0 0 0 [swapper] > > 0 0 1 18d30240 RU 0.0 0 0 [swapper] > > 0 0 2 18d38340 RU 0.0 0 0 [swapper] > > 0 0 3 18d40440 RU 0.0 0 0 [swapper] > > 0 0 4 18d48540 RU 0.0 0 0 [swapper] > 1 0 1 18d18040 IN 0.2 2244 1020 init > ... > > And "bt -a" shows: > > PID: 0 TASK: 800ef0 CPU: 0 COMMAND: "swapper" > LOWCORE INFO: > -psw : 0x0706000180000000 0x0000000000115564 > -function : vtime_stop_cpu at 115564 > -prefix : 0x18d28000 > -cpu timer: 0x7fff00c1 0x00c584ef > ... > > PID: 0 TASK: 18d30240 CPU: 1 COMMAND: "swapper" > LOWCORE INFO: > -psw : 0x0706000180000000 0x0000000000115564 > -function : vtime_stop_cpu at 115564 > ... > > PID: 0 TASK: 18d38340 CPU: 2 COMMAND: "swapper" > #0 [18d3feb8] ret_from_fork at 117e12 > ... > > PID: 0 TASK: 18d40440 CPU: 3 COMMAND: "swapper" > #0 [18d47eb8] ret_from_fork at 117e12 > ... > > PID: 0 TASK: 18d48540 CPU: 4 COMMAND: "swapper" > LOWCORE INFO: > -psw : 0x0706000180000000 0x0000000000115564 > -function : vtime_stop_cpu at 115564 > -prefix : 0x1416a000 > > Michael -- Crash-utility mailing list Crash-utility@xxxxxxxxxx https://www.redhat.com/mailman/listinfo/crash-utility
