linux-kernel - Re: [RFC] Removing b_end

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Message-ID: <20201025185849.GJ20115@casper.infradead.org>
Date:   Sun, 25 Oct 2020 18:58:49 +0000
From:   Matthew Wilcox <willy@...radead.org>
To:     "Theodore Y. Ts'o" <tytso@....edu>
Cc:     linux-block@...r.kernel.org, Christoph Hellwig <hch@....de>,
        linux-kernel@...r.kernel.org, linux-fsdevel@...r.kernel.org
Subject: Re: [RFC] Removing b_end_io

On Sun, Oct 25, 2020 at 11:56:52AM -0400, Theodore Y. Ts'o wrote:
> On Sun, Oct 25, 2020 at 04:44:38AM +0000, Matthew Wilcox wrote:
> > @@ -3068,6 +3069,12 @@ static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
> >  	}
> >  
> >  	submit_bio(bio);
> > +}
> > +
> > +static int submit_bh_wbc(int op, int op_flags, struct buffer_head *bh,
> > +			 enum rw_hint write_hint, struct writeback_control *wbc)
> > +{
> > +	__bh_submit(bh, op | op_flags, write_hint, wbc, end_bio_bh_io_sync);
> >  	return 0;
> >  }
> >
> 
> I believe this will break use cases where the file system sets
> bh->b_end_io and then calls submit_bh(), which then calls
> submit_bh_wbc().  That's because with this change, calls to
> submit_bh_wbc() --- include submit_bh() --- ignores bh->b_end_io and
> results in end_bio_bh_io_sync getting used.

I think you're confused between the two end_ios.  The final argument
to bh_submit() and __bh_submit() is a bio_end_io_t.  end_bio_bh_io_sync()
calls bh->b_end_io.