Re: [Patch] fs: remove a useless BUG()

[Cong Wang]

Andrew Morton wrote:
> On Mon, 30 Nov 2009 21:34:14 -0500
> Amerigo Wang <amwang@xxxxxxxxxx> wrote:
>
> > This BUG() is suspicious, it makes its following statements
> > unreachable, and it seems to be useless, since the caller
> > of this function already handles the failure properly.
> > Remove it.
> >
> > Signed-off-by: WANG Cong <amwang@xxxxxxxxxx>
> > Cc: Alexander Viro <viro@xxxxxxxxxxxxxxxxxx>
> > Cc: Jens Axboe <jens.axboe@xxxxxxxxxx>
> > Cc: Nick Piggin <npiggin@xxxxxxx>
> > Cc: "Theodore Ts'o" <tytso@xxxxxxx>
> >
> > ---
> > diff --git a/fs/buffer.c b/fs/buffer.c
> > index 6fa5302..ac111d7 100644
> > --- a/fs/buffer.c
> > +++ b/fs/buffer.c
> > @@ -1041,7 +1041,6 @@ grow_dev_page(struct block_device *bdev, sector_t block,
> >  	return page;
> >  
> >  failed:
> > -	BUG();
> >  	unlock_page(page);
> >  	page_cache_release(page);
> >  	return NULL;
>
> The caller doesn't handle this properly.  If we return zero here,
> grow_buffers() will say sheesh and will retry and the kernel goes into
> an infinite retry loop.
>
> If there is a blockdev page which is sitting in pagecache and for some
> reason it has buffers and we cannot release them, we're kind of stuck
> and don't know what to do.  Going BUG() is a decent thing to do here.
>
> I don't think I've ever seen a report of the BUG triggering.  It could
> happen as a result of memory corruption or a missed bh_put() or
> whatever.

Oh, good explanation!

> I think a better patch would be to remove the
> unlock_page()/page_cache_release(), add a comment (culled from the
> above) and leave the BUG() there.

Ok, I will prepare a patch tomorrow.

Thanks!


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