Re: [PATCH v3 1/9] perf tools: add parse events append error

[Jiri Olsa]

On Mon, Oct 28, 2019 at 02:06:24PM -0700, Ian Rogers wrote:
> On Mon, Oct 28, 2019 at 12:32 PM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> >
> > On Fri, Oct 25, 2019 at 08:14:36AM -0700, Ian Rogers wrote:
> > > On Fri, Oct 25, 2019 at 12:58 AM Jiri Olsa <jolsa@xxxxxxxxxx> wrote:
> > > >
> > > > On Thu, Oct 24, 2019 at 12:01:54PM -0700, Ian Rogers wrote:
> > > > > Parse event error handling may overwrite one error string with another
> > > > > creating memory leaks and masking errors. Introduce a helper routine
> > > > > that appends error messages and avoids the memory leak.
> > > > >
> > > > > A reproduction of this problem can be seen with:
> > > > >   perf stat -e c/c/
> > > > > After this change this produces:
> > > > > event syntax error: 'c/c/'
> > > > >                        \___ unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: unknown term (previous error: Cannot find PMU `c'. Missing kernel support?)(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,pc,in_tx,edge,any,offcore_rsp,in_tx_cp,ldlat,inv,umask,frontend,cmask,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))(help: valid terms: event,filter_rem,filter_opc0,edge,filter_isoc,filter_tid,filter_loc,filter_nc,inv,umask,filter_opc1,tid_en,thresh,filter_all_op,filter_not_nm,filter_state,filter_nm,config,config1,config2,name,period,percore))
> > > >
> > > >
> > > > hum... I'd argue that the previous state was better:
> > > >
> > > > [jolsa@krava perf]$ ./perf stat -e c/c/
> > > > event syntax error: 'c/c/'
> > > >                        \___ unknown term
> > > >
> > > >
> > > > jirka
> > >
> > > I am agnostic. We can either have the previous state or the new state,
> > > I'm keen to resolve the memory leak. Another alternative is to warn
> > > that multiple errors have occurred before dropping or printing the
> > > previous error. As the code is shared in memory places the approach
> > > taken here was to try to not conceal anything that could potentially
> > > be useful. Given this, is the preference to keep the status quo
> > > without any warning?
> >
> > if the other alternative is string above, yes.. but perhaps
> > keeping just the first error would be the best way?
> >
> > here it seems to be the:
> >    "Cannot find PMU `c'. Missing kernel support?)(help: valid..."
> 
> I think this is a reasonable idea. I'd propose doing it as an
> additional patch, the purpose of this patch is to avoid a possible
> memory leak. I can write the patch and base it on this series.
> To resolve the issue, I'd add an extra first error to the struct
> parse_events_error. All callers would need to be responsible for
> cleaning this up when present, which is why I'd rather not make it
> part of this patch.
> Does this sound reasonable?

yep, sounds good

jirka