Re: [PATCH] f2fs: fix the assign logic of iocb

[Masami Hiramatsu (Google) <mhiramat@kernel.org>]

On Fri, 21 Oct 2022 10:30:46 +0530
Pavan Kondeti <quic_pkondeti@quicinc.com> wrote:

> Hi Mukesh,
> 
> On Wed, Oct 19, 2022 at 09:47:57PM +0530, Mukesh Ojha wrote:
> > commit 18ae8d12991b ("f2fs: show more DIO information in tracepoint")
> > introduces iocb field in 'f2fs_direct_IO_enter' trace event
> > And it only assigns the pointer and later it accesses its field
> > in trace print log.
> > 
> > Fix it by correcting data type and memcpy the content of iocb.
> > 
> > Fixes: 18ae8d12991b ("f2fs: show more DIO information in tracepoint")
> > Signed-off-by: Mukesh Ojha <quic_mojha@quicinc.com>
> > ---
> >  include/trace/events/f2fs.h | 10 +++++-----
> >  1 file changed, 5 insertions(+), 5 deletions(-)
> > 
> > diff --git a/include/trace/events/f2fs.h b/include/trace/events/f2fs.h
> > index c6b3724..7727ec9 100644
> > --- a/include/trace/events/f2fs.h
> > +++ b/include/trace/events/f2fs.h
> > @@ -940,7 +940,7 @@ TRACE_EVENT(f2fs_direct_IO_enter,
> >  	TP_STRUCT__entry(
> >  		__field(dev_t,	dev)
> >  		__field(ino_t,	ino)
> > -		__field(struct kiocb *,	iocb)
> > +		__field_struct(struct kiocb,	iocb)
> >  		__field(unsigned long,	len)
> >  		__field(int,	rw)
> >  	),
> > @@ -948,17 +948,17 @@ TRACE_EVENT(f2fs_direct_IO_enter,
> >  	TP_fast_assign(
> >  		__entry->dev	= inode->i_sb->s_dev;
> >  		__entry->ino	= inode->i_ino;
> > -		__entry->iocb	= iocb;
> > +		 memcpy(&__entry->iocb, iocb, sizeof(*iocb));
> >  		__entry->len	= len;
> >  		__entry->rw	= rw;
> >  	),
> >  
> 
> Why copy the whole structure (48 bytes)? cache the three members you
> need.

+1. If this only prints ki_pos, ki_flags and ki_ioprio, I recommend you
to save those 3 fields to the entry. It should not expose in-kernel
data structure because it can be changed.

Thank you,

> 
> Thanks,
> Pavan


-- 
Masami Hiramatsu (Google) <mhiramat@kernel.org>