Re: [PATCH 2/6] pstore: Add event tracing support

[Sai Prakash Ranjan]

On 9/17/2018 11:08 PM, Stephen Boyd wrote:
> Quoting Sai Prakash Ranjan (2018-09-11 03:46:01)
> > On 9/9/2018 1:57 AM, Sai Prakash Ranjan wrote:
> > > +void notrace pstore_event_call(struct trace_event_buffer *fbuffer)
> > > +{
> > > +     struct trace_iterator *iter;
> > > +     struct trace_seq *s;
> > > +     struct trace_event_call *event_call;
> > > +     struct pstore_record record;
> > > +     struct trace_event *event;
> > > +     struct seq_buf *seq;
> > > +     unsigned long flags;
> > > +
> > > +     if (!psinfo)
> > > +             return;
> > > +
> > > +     if (unlikely(oops_in_progress))
> > > +             return;
> > > +
> > > +     pstore_record_init(&record, psinfo);
> > > +     record.type = PSTORE_TYPE_EVENT;
> > > +
> > > +     iter = kmalloc(sizeof(*iter), GFP_KERNEL);
> > > +     if (!iter)
> > > +             return;
> > > +
> > > +     event_call = fbuffer->trace_file->event_call;
> > > +     if (!event_call || !event_call->event.funcs ||
> > > +         !event_call->event.funcs->trace)
> > > +             goto fail_event;
> > > +
> > > +     event = &fbuffer->trace_file->event_call->event;
> > > +
> > > +     spin_lock_irqsave(&psinfo->buf_lock, flags);
> > > +
> > > +     trace_seq_init(&iter->seq);
> > > +     iter->ent = fbuffer->entry;
> > > +     event_call->event.funcs->trace(iter, 0, event);
> > > +     trace_seq_putc(&iter->seq, 0);
> > > +
> > > +     if (seq->size > psinfo->bufsize)
> > > +             seq->size = psinfo->bufsize;
> > > +
> > > +     s = &iter->seq;
> > > +     seq = &s->seq;
> > > +
> > > +     record.buf = (char *)(seq->buffer);
> > > +     record.size = seq->len;
> > > +     psinfo->write(&record);
> > > +
> > > +     spin_unlock_irqrestore(&psinfo->buf_lock, flags);
> > > +
> > > +fail_event:
> > > +     kfree(iter);
> > > +}
> > > +
> >
> > When tracing sched events on sdm845 mtp, I hit below bug repeatedly.
> > Seems like pstore_event_call can be called in atomic context.
> > I will respin the below fix in next version of the patch.
> > Reviews on other parts would be appreciated, thanks.
> >
> > diff --git a/fs/pstore/ftrace.c b/fs/pstore/ftrace.c
> > index d47dc93ac098..a497cf782ee8 100644
> > --- a/fs/pstore/ftrace.c
> > +++ b/fs/pstore/ftrace.c
> > @@ -73,6 +73,7 @@ void notrace pstore_event_call(struct
> > trace_event_buffer *fbuffer)
> >           struct trace_event *event;
> >           struct seq_buf *seq;
> >           unsigned long flags;
> > +       gfp_t gfpflags;
> >
> >           if (!psinfo)
> >                   return;
> > @@ -83,7 +84,9 @@ void notrace pstore_event_call(struct
> > trace_event_buffer *fbuffer)
> >           pstore_record_init(&record, psinfo);
> >           record.type = PSTORE_TYPE_EVENT;
> >
> > -       iter = kmalloc(sizeof(*iter), GFP_KERNEL);
> > +       gfpflags = (in_atomic() || irqs_disabled()) ? GFP_ATOMIC :
> > GFP_KERNEL;
> > +

Hi Stephen

Thanks for the comments.

> Do you need to allocate at all? Can you throw the iter on the stack?

Yes since we need to copy the contents to pstore buffer.

> Using in_atomic() and irqs_disabled() to figure out if an atomic or a
> non-atomic allocation should be used is not a good solution.

I took reference from a similar use by graph_trace_open() which can be 
called in atomic context via ftrace_dump(). I am open to correct this if 
there is some other way.

Sai

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