Re: [PATCH] nilfs2: remove double bio_put() in nilfs_end_bio_write() for BIO_EOPNOTSUPP error

[Vyacheslav Dubeyko <slava@dubeyko.com>]

Hi Ryusuke,

On Tue, 2013-07-23 at 03:24 +0900, Ryusuke Konishi wrote:

[snip]
> 
> Thank you for following the issue.  I reviewed the code around bio.
> 
> In conclusion, Dan Carpenter's patch looks correct because
> nilfs_segbuf_submit_bio() does not increment the number of flying bio
> (segbuf->sb_nbio) for EOPNOTSUPP/BIO_EOPNOTSUPP case.
> 

I worry that nilfs_end_bio_write() is called asynchronously. And, as I
understand, the BIO_EOPNOTSUPP flag is set during nilfs_end_bio_write()
call. It means for me that sometimes segbuf->sb_nbio will be not
incremented in nilfs_segbuf_submit_bio() but sometimes this field can be
incremented and for BIO_EOPNOTSUPP case.

> If nilfs_end_bio_write() function reaches the complete() call for the
> EOPNOTSUPP/BIO_EOPNOTSUPP case (as the current implementation), the
> number of complete() calls and that of wait_for_complete() will not
> balance.
> 

I think that it is dangerous to return without complete() call because
of asynchronous nature of nilfs_end_bio_write() call.

What do you think?

With the best regards,
Vyacheslav Dubeyko.

> Do you have a comment?
> 
> Regards,
> Ryusuke Konishi
> 
> > ---
> >  fs/nilfs2/segbuf.c |    3 +--
> >  1 file changed, 1 insertion(+), 2 deletions(-)
> > 
> > diff --git a/fs/nilfs2/segbuf.c b/fs/nilfs2/segbuf.c
> > index dc9a913..5bacf46 100644
> > --- a/fs/nilfs2/segbuf.c
> > +++ b/fs/nilfs2/segbuf.c
> > @@ -345,8 +345,7 @@ static void nilfs_end_bio_write(struct bio *bio, int err)
> >  
> >  	if (err == -EOPNOTSUPP) {
> >  		set_bit(BIO_EOPNOTSUPP, &bio->bi_flags);
> > -		bio_put(bio);
> > -		/* to be detected by submit_seg_bio() */
> > +		/* to be detected by nilfs_segbuf_submit_bio() */
> >  	}
> >  
> >  	if (!uptodate)
> > -- 
> > 1.7.9.5
> > 
> > 
> > 
> > --
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