----- Original Message -----
> On Tue, Oct 09, 2018 at 09:39:10AM -0400, Dave Anderson wrote:
> >
> >
> > ----- Original Message -----
> > > 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
> >
> >
> >
> > Ok, the most recent 4.18 kernel I have on hand is this one:
> >
> > crash> sys | grep RELEASE
> > RELEASE: 4.18.0-20.el8.x86_64
> > crash>
> >
> > and its debuginfo data contains the "thread_union" information:
> >
> > crash> thread_union
> > union thread_union {
> > struct task_struct task;
> > unsigned long stack[2048];
> > }
> > SIZE: 16384
> > crash>
> >
> > but if it did not, then code should then calculate the stack
> > size from the difference between the "__start_init_task" and
> > "__end_init_task" symbols:
> >
> > crash> sym __start_init_task
> > ffffffffa7800000 (D) __start_init_task
> > crash> sym __end_init_task
> > ffffffffa7804000 (D) __end_init_task
> > crash>
> >
> > Does your kernel not show/contain those 2 symbols?
> >
> Sure, my test kernel contains these 2 symbols.
>
> crash> sys | grep RELEASE
> RELEASE: 4.18.0-1-default+
> crash> thread_union
> crash: command not found: thread_union
> crash> struct thread_union
> struct: invalid data structure reference: thread_union
> crash> sym __start_init_task
> ffffffff82000000 (D) __start_init_task
> crash> sym __end_init_task
> ffffffff82004000 (D) __end_init_task
>
> Agree with you, Automatic calculation stack size from the difference
> between__start_init_task and __end_init_task should be better.
> Calculating and assignning stack size should be add into "x86_64_init", Do
> you think so?
No, because the calculation is being done in an architecture-neutral manner
by task_init(), here in task.c:
437 if (VALID_SIZE(task_union) && (SIZE(task_union) != STACKSIZE())) {
438 error(WARNING, "\nnon-standard stack size: %ld\n",
439 len = SIZE(task_union));
440 machdep->stacksize = len;
441 } else if (VALID_SIZE(thread_union) &&
442 ((len = SIZE(thread_union)) != STACKSIZE())) {
443 machdep->stacksize = len;
444 } else if (!VALID_SIZE(thread_union) && !VALID_SIZE(task_union)) {
445 if (kernel_symbol_exists("__start_init_task") &&
446 kernel_symbol_exists("__end_init_task")) {
447 len = symbol_value("__end_init_task");
448 len -= symbol_value("__start_init_task");
449 ASSIGN_SIZE(thread_union) = len;
450 machdep->stacksize = len;
451 }
452 }
I see that "thread_union" is not found in your debuginfo data, but I don't understand
how your kernel gets past the second "else" segment above where the __start_init_task
and __end_init_task symbol values are checked.
Dave
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