Re: [RFC PATCH] Add TRACE_IRQFLAGS_SUPPORT, LOCKDEP_SUPPORT then enable ftrace for ia64

[Tony Luck <tony.luck@xxxxxxxxx>]

On Wed, Dec 9, 2009 at 12:52 AM, Luming Yu <luming.yu@xxxxxxxxx> wrote:
> Commenting out the change make -32 Lockdep kernel boot.
>
> Tony, please let me know whether you can reproduce..

Yes.  Commenting this out makes the system bootable for me.

> kernel/lockdep.c
> static int save_trace(struct stack_trace *trace)
> {
>        trace->nr_entries = 0;
>        trace->max_entries = MAX_STACK_TRACE_ENTRIES - nr_stack_trace_entries;
>        trace->entries = stack_trace + nr_stack_trace_entries;
>
>        trace->skip = 3;
>
>        save_stack_trace(trace);
> #if 0
>
>        /*
>         * Some daft arches put -1 at the end to indicate its a full trace.
>         *
>         * <rant> this is buggy anyway, since it takes a whole extra entry so a
>         * complete trace that maxes out the entries provided will be reported
>         * as incomplete, friggin useless </rant>
>         */
>        if (trace->entries[trace->nr_entries-1] == ULONG_MAX)
>                trace->nr_entries--;
> #endif

This happens because ia64 save_stack_trace() is currently an empty stub, so it
doesn't set trace->nr_entries.

Options:
1) Add trace->nr_entries = 1; to ia64 stub.
2) Change the generic code to defend against an unexpected failure in
save_stack_trace()

       if (trace->nr_entries > 0 &&
           trace->entries[trace->nr_entries-1] == ULONG_MAX)
               trace->nr_entries--;
3) Delete the code in the "daft"[1] architectures, and drop this hunk
from the generic code.

-Tony

[1] arm, parisc, s390, sh, x86
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