Re: [Crash-utility] [PATCH] cmdline: Add a new "--machdep stacksize=<value>".

On Mon, Oct 01, 2018 at 09:37:10AM -0400, Dave Anderson wrote: > > > ----- Original Message ----- > > Implemented support for 16k stack size that was introduced by commit > > 6538b8ea886e472f4431db8ca1d60478f838d14b titled "x86_64: expand kernel > > stack to 16K". > > Without the patch, kernels has 16k stack, leading to errors in commands > > such as "bt" and any command regarding 8K stack. > > Add a new "--machdep stacksize=<value>" option that can be used to > > override the default machdep->stacksize value which is 8k. > > The x86_64 default value of 8K is basically a leftover value that each of > the architectures originally used for setting machdep->stacksize. But for > quite some time now, those values should get overridden later on here > in task_init(): > > STRUCT_SIZE_INIT(task_union, "task_union"); > STRUCT_SIZE_INIT(thread_union, "thread_union"); > > if (VALID_SIZE(task_union) && (SIZE(task_union) != STACKSIZE())) { > error(WARNING, "\nnon-standard stack size: %ld\n", > len = SIZE(task_union)); > machdep->stacksize = len; > } else if (VALID_SIZE(thread_union) && > ((len = SIZE(thread_union)) != STACKSIZE())) { > machdep->stacksize = len; > } else if (!VALID_SIZE(thread_union) && !VALID_SIZE(task_union)) { > if (kernel_symbol_exists("__start_init_task") && > kernel_symbol_exists("__end_init_task")) { > len = symbol_value("__end_init_task"); > len -= symbol_value("__start_init_task"); > ASSIGN_SIZE(thread_union) = len; > machdep->stacksize = len; > } > } > I compiled latest kernel and latest crash and run a qemu guest machine with the latest compliled kernel image. In this case, STRUCT_SIZE_INIT initialized size_table.task_union and size_table.thread_union with -1. So machdep->stacksize did NOT get overridden. > As of Linux 4.18 at least, x86_64 still uses the thread_union declaration. > For example: > > crash> thread_union > union thread_union { > struct task_struct task; > unsigned long stack[2048]; > } > SIZE: 16384 > crash> > > On what kernel version are you seeing the obsolete 8k stacksize being used? > What does the command above show on your system? kernel version is upstream Linux 4.18 (commit#94710cac0ef4ee177a63b5227664b38c95bbf703) (git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git). "bt" command in crash shows "bt: invalid RSP: ffffc9000069bc08 bt->stackbase/stacktop: ffffc90000698000/ffffc9000069a000 cpu: 0". BestRegards Sean

> > Thanks, > Dave > > > > > > > > Signed-off-by: Sean Fu <fxinrong(a)gmail.com&gt; > > --- > > x86_64.c | 9 +++++++++ > > 1 file changed, 9 insertions(+) > > > > diff --git a/x86_64.c b/x86_64.c > > index 7d01140..1798f05 100644 > > --- a/x86_64.c > > +++ b/x86_64.c > > @@ -5716,6 +5716,15 @@ parse_cmdline_args(void) > > continue; > > } > > } > > + } else if (STRNEQ(arglist[i], "stacksize=")) { > > + p = arglist[i] + strlen("stacksize="); > > + if (strlen(p)) { > > + value = stol(p, RETURN_ON_ERROR|QUIET, &errflag); > > + if (!errflag) { > > + machdep->stacksize = value; > > + continue; > > + } > > + } > > } > > > > error(WARNING, "ignoring --machdep option: %s\n", arglist[i]); > > -- > > 2.6.2 > > > >