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To:     Anton Vorontsov <anton@enomsg.org>, Arnd Bergmann <arnd@arndb.de>,
        Catalin Marinas <catalin.marinas@arm.com>,
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        Sai Prakash Ranjan <saiprakash.ranjan@codeaurora.org>,
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References: <cover.1536430404.git.saiprakash.ranjan@codeaurora.org>
 <b9b60ff2864a17fb05481aa33f90114ab051d6ce.1536430404.git.saiprakash.ranjan@codeaurora.org>
 <444d7b13-2653-ba0e-e9e6-a448fded2a77@codeaurora.org>
Message-ID: <153720590027.119890.15984895820368075914@swboyd.mtv.corp.google.com>
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Subject: Re: [PATCH 2/6] pstore: Add event tracing support
Date:   Mon, 17 Sep 2018 10:38:20 -0700
Sender: linux-kernel-owner@vger.kernel.org
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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 =3D PSTORE_TYPE_EVENT;
> > +
> > +     iter =3D kmalloc(sizeof(*iter), GFP_KERNEL);
> > +     if (!iter)
> > +             return;
> > +
> > +     event_call =3D fbuffer->trace_file->event_call;
> > +     if (!event_call || !event_call->event.funcs ||
> > +         !event_call->event.funcs->trace)
> > +             goto fail_event;
> > +
> > +     event =3D &fbuffer->trace_file->event_call->event;
> > +
> > +     spin_lock_irqsave(&psinfo->buf_lock, flags);
> > +
> > +     trace_seq_init(&iter->seq);
> > +     iter->ent =3D fbuffer->entry;
> > +     event_call->event.funcs->trace(iter, 0, event);
> > +     trace_seq_putc(&iter->seq, 0);
> > +
> > +     if (seq->size > psinfo->bufsize)
> > +             seq->size =3D psinfo->bufsize;
> > +
> > +     s =3D &iter->seq;
> > +     seq =3D &s->seq;
> > +
> > +     record.buf =3D (char *)(seq->buffer);
> > +     record.size =3D 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 =3D PSTORE_TYPE_EVENT;
> =

> -       iter =3D kmalloc(sizeof(*iter), GFP_KERNEL);
> +       gfpflags =3D (in_atomic() || irqs_disabled()) ? GFP_ATOMIC : =

> GFP_KERNEL;
> +

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

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.