Re: [Crash-utility] [PATCH] crash: Do not use bt -t flag in panic_search()

On Thu, 6 Aug 2015 11:25:29 -0400 (EDT) Dave Anderson <anderson(a)redhat.com&gt; wrote: > Re: your dumpfile where the erroneous "panic" address in a random user > task's exception frame register set gets picked up by mistake. > > Your original patch request modified the "bt" command used for the > kernel stack searches in panic_search(). But that piece of code > is the last-ditch effort for finding a panic task, which follows > this path: > > get_panic_context() > panic_search() > get_dumpfile_panic_task() > get_kdump_panic_task() (requires kdump "crashing_cpu" symbol) > get_diskdump_panic_task() (requires kdump "crashing_cpu" symbol) On s390 we don't have the "crashing_cpu" symbol in the kernel. > get_active_set_panic_task() (bt -r raw stack dump of active cpus) > ... > > Only if all of the above fail, does panic_search() initiate the > exhaustive walkthrough of all kernel stacks for evidence. > > Since you have gotten that far, I'm wondering whether your > target dumpfile with the faulty "panic" address is from an > s390x "live dump"? In that case, there can never be any task > with any such evidence, making the backtrace search a waste of > time to begin with. The "problem" dump is a s390 stand-alone dump of a hanging system. All CPUs have been in "psw_idle" when the dump was generated: PID: 0 TASK: c50f38 CPU: 0 COMMAND: "swapper/0" LOWCORE INFO: -psw : 0x0706c00180000000 0x000000000084410e -function : psw_idle at 84410e [snip] #0 [00c1fe70] arch_cpu_idle at 104d4a #1 [00c1fe90] cpu_startup_entry at 180430 #2 [00c1fee8] start_kernel at d1fb10 #3 [00c1ff60] _stext at 100020 > > And if so, I'm thinking that since s390x will have set LIVE_DUMP > flag set, if get_dumpfile_panic_task() returns NO_TASK, then > panic_search() should just return a NULL to get_panic_context() > if it's a live dump, which will just default to the idle task on > cpu 0. Although it does not solve the above problem it makes sense for live dumps. What about the following patch? --- crash: do not search panic tasks for live dumps Always return "NO_TASK" if the "LIVE_DUMP" flag is set because live dumps cannot have a panic task. Signed-off-by: Michael Holzheu <holzheu(a)linux.vnet.ibm.com&gt; --- task.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) --- a/task.c +++ b/task.c @@ -6726,7 +6726,10 @@ get_dumpfile_panic_task(void) { ulong task; - if (NETDUMP_DUMPFILE()) { + if (pc->flags2 & LIVE_DUMP) { + /* No panic task because system itself created the dump */ + return NO_TASK; + } else if (NETDUMP_DUMPFILE()) { task = pc->flags & REM_NETDUMP ? tt->panic_task : get_netdump_panic_task(); if (task)