[Crash-utility] [PATCH] Fix machdep->HZ calculation for kernel versions > 2.6.0

[HAGIO KAZUHITO(萩尾 一仁)]

-----Original Message-----
> 在 2021年04月23日 17:44, HAGIO KAZUHITO(萩尾　一仁) 写道:
> > -----Original Message-----
> >>> As for the 'write_expire' way, I found that it can be printed after
> >>> "set scope dd_init_queue" or "set scope deadline_init_queue" on old kernels.
> >>>
> >>> crash> p write_expire
> >>> No symbol "write_expire" in current context.
> >>> p: gdb request failed: p write_expire
> >>> crash> set scope dd_init_queue
> >>> scope: ffffffffa43e3f80 (dd_init_queue)
> >>> crash> p write_expire
> >>> $1 = 5000
> >>>
> >>> Maybe we can make use of gdb_set_crash_scope() and gdb_pass_through() to
> >>> get this value?
> >>>
> >>
> >> The 'write_expire' is a static variable, which needs to get its value from
> >> gdb. Seems that it is a bit complicated.
> >>
> >> But It's worth having a try.
> >
> > The following is a draft patch.  It worked for some dumpfiles I have
> > from 2.6.16 to 5.11 including RHEL8.0 one.  What do you think?
> >
> 
> Good idea. Could you please post a formal patch about this change?

Yes, I will.

> 
> BTW: is that possible to remove the 'cfq_slice_async'?

I don't think so, I would like to keep this with Martin's patch [1], because
these HZ calculations depend on kernel configs, removing it can cause a
regression for vmcores that do not have the 'write_expire'.

And that 'write_expire' way is a little tricky one and the crash utility
has not used a similar way (using gdb_set_crash_scope()) to get a required
value before (I see gdb_set_crash_scope() in trace.c though [2]), so I'd
like to set the 'cfq_slice_async' way above it, i.e.:

  if ((THIS_KERNEL_VERSION < LINUX(4,8,0)) &&
      symbol_exists("cfq_slice_async")) {
      ...
  } else if ((symbol_exists("dd_init_queue") &&
      ...

[1] https://listman.redhat.com/archives/crash-utility/2021-April/msg00063.html
[2] https://github.com/fujitsu/crash-trace/blob/master/trace.c#L223

Thanks,
Kazu

> 
> Thanks.
> Lianbo
> 
> > diff --git a/task.c b/task.c
> > index 423cd454502b..654df6b1220c 100644
> > --- a/task.c
> > +++ b/task.c
> > @@ -417,7 +417,33 @@ task_init(void)
> >
> >  	STRUCT_SIZE_INIT(cputime_t, "cputime_t");
> >
> > -	if (symbol_exists("cfq_slice_async")) {
> > +	if ((symbol_exists("dd_init_queue") &&
> > +	    gdb_set_crash_scope(symbol_value("dd_init_queue"), "dd_init_queue")) ||
> > +	    (symbol_exists("deadline_init_queue") &&
> > +	    gdb_set_crash_scope(symbol_value("deadline_init_queue"), "deadline_init_queue"))) {
> > +		char buf[BUFSIZE];
> > +		uint write_expire = 0;
> > +
> > +		open_tmpfile();
> > +		sprintf(buf, "printf \"%%d\", write_expire");
> > +		if (gdb_pass_through(buf, pc->tmpfile, GNU_RETURN_ON_ERROR)) {
> > +			rewind(pc->tmpfile);
> > +			while (fgets(buf, BUFSIZE, pc->tmpfile)) {
> > +				sscanf(buf, "%d", &write_expire);
> > +			}
> > +		}
> > +		close_tmpfile();
> > +
> > +		if (write_expire) {
> > +			machdep->hz = write_expire / 5;
> > +			if (CRASHDEBUG(2))
> > +				fprintf(fp, "write_expire exists: setting hz to %d\n",
> > +					machdep->hz);
> > +		}
> > +		fprintf(fp, "write_expire = %d, machdep->hz = %d\n", write_expire, machdep->hz);
> > +		gdb_set_crash_scope(0, NULL);
> > +
> > +	} else if (symbol_exists("cfq_slice_async")) {
> >  		uint cfq_slice_async;
> >
> >  		get_symbol_data("cfq_slice_async", sizeof(int),
> >