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SubjectRe: [patch] add /proc/pid/stack to dump task's stack trace
On Fri, Nov 07, 2008 at 09:32:49AM +0100, Ingo Molnar wrote:
>
> * Alexey Dobriyan <adobriyan@gmail.com> wrote:
>
> > On Fri, Nov 07, 2008 at 08:59:25AM +0100, Ingo Molnar wrote:
> > >
> > > * Ingo Molnar <mingo@elte.hu> wrote:
> > >
> > > > > > + * buffer size used for proc read. See proc_info_read().
> > > > > > + * 4K page size but our output routines use some slack for overruns
> > > > > > + */
> > > > > > +#define PROC_BLOCK_SIZE (3*1024)
> > > >
> > > > That sounds like a proper limit - the hard limit for this particular
> > > > printout function is 4096-170, so we are well within the
> > > > PROC_BLOCK_SIZE range.
> > >
> > > ok, i've added Ken's patch to tip/core/stacktrace and started testing
> > > it.
> > >
> > > Alexey, i've added your Acked-by because you appeared to like the
> > > patch - let me know if i should remove it.
> >
> > Of course, I don't like it!
> >
> > Switch to seqfiles, add entry in TID table as well.
> >
> > The idea is good, though.
>
> oh well - Ken, could you please switch it to seqfiles?
>
> It should be something like this to convert the currently sweet and
> trivial function into a much more complex seqfile iterator splitup:
>
> - the ::start method does the kmalloc of a loop state structure like
> this:
>
> {
> struct stack_trace backtrace;
> unsigned long entries[MAX_STACK_TRACE_DEPTH];
>
> int iterator;
> }
>
> and saves the trace. (struct stack_trace trace can be on-stack, it's
> only needed for the save_stack_trace() - and we keep the entries
> after that.)
>
> - the ::stop method does the kfree of the loop state.
>
> - the ::show method prints a single line, based on ->entries[->iterator]
>
> - the ::next method does ->iterator++, and returns NULL if iterator
> reaches ->backtrace.nr_entries.
>
> it will be more source code, larger kernel image, it will be more
> fragile and will be harder to review, and it wont actually matter in
> practice because 99.9999% of the backtraces we care about have a size
> smaller than 3K. (and where they get larger clipping them to the first
> 3K is perfectly fine)

Or you can do all of this in ->show(), without start/next/stop:

for (i = 0; i < N; i++)
seq_printf(m, "[<%p>] %pS\n", x, x);


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