Re: [PATCH] xfs: shutdown on failure to add page to log bio

[Brian Foster <bfoster@redhat.com>]

On Tue, Mar 24, 2020 at 10:18:59AM -0700, Darrick J. Wong wrote:
> On Tue, Mar 24, 2020 at 12:57:00PM -0400, Brian Foster wrote:
> > If the bio_add_page() call fails, we proceed to write out a
> > partially constructed log buffer. This corrupts the physical log
> > such that log recovery is not possible. Worse, persistent
> > occurrences of this error eventually lead to a BUG_ON() failure in
> > bio_split() as iclogs wrap the end of the physical log, which
> > triggers log recovery on subsequent mount.
> > 
> > Rather than warn about writing out a corrupted log buffer, shutdown
> > the fs as is done for any log I/O related error. This preserves the
> > consistency of the physical log such that log recovery succeeds on a
> > subsequent mount. Note that this was observed on a 64k page debug
> > kernel without upstream commit 59bb47985c1d ("mm, sl[aou]b:
> > guarantee natural alignment for kmalloc(power-of-two)"), which
> > demonstrated frequent iclog bio overflows due to unaligned (slab
> > allocated) iclog data buffers.
> 
> Fixes: tag?
> 

I suppose you could argue it fixes commit 79b54d9bfcdcd ("xfs: use bios
directly to write log buffers"), but I didn't include a tag because this
is not really fixing a reproducible bug. It's fixing up the error
handling based on a bad combination of patches in a distro kernel.
Perhaps I'm just not clear on when we do or don't want a fixes tag..?

Brian

> Otherwise, looks ok to me.
> 
> --D
> 
> > Signed-off-by: Brian Foster <bfoster@redhat.com>
> > ---
> >  fs/xfs/xfs_log.c | 14 ++++++++++----
> >  1 file changed, 10 insertions(+), 4 deletions(-)
> > 
> > diff --git a/fs/xfs/xfs_log.c b/fs/xfs/xfs_log.c
> > index 2a90a483c2d6..ebb6a5c95332 100644
> > --- a/fs/xfs/xfs_log.c
> > +++ b/fs/xfs/xfs_log.c
> > @@ -1705,16 +1705,22 @@ xlog_bio_end_io(
> >  
> >  static void
> >  xlog_map_iclog_data(
> > -	struct bio		*bio,
> > -	void			*data,
> > +	struct xlog_in_core	*iclog,
> >  	size_t			count)
> >  {
> > +	struct xfs_mount	*mp = iclog->ic_log->l_mp;
> > +	struct bio		*bio = &iclog->ic_bio;
> > +	void			*data = iclog->ic_data;
> > +
> >  	do {
> >  		struct page	*page = kmem_to_page(data);
> >  		unsigned int	off = offset_in_page(data);
> >  		size_t		len = min_t(size_t, count, PAGE_SIZE - off);
> >  
> > -		WARN_ON_ONCE(bio_add_page(bio, page, len, off) != len);
> > +		if (bio_add_page(bio, page, len, off) != len) {
> > +			xfs_force_shutdown(mp, SHUTDOWN_LOG_IO_ERROR);
> > +			break;
> > +		}
> >  
> >  		data += len;
> >  		count -= len;
> > @@ -1762,7 +1768,7 @@ xlog_write_iclog(
> >  	if (need_flush)
> >  		iclog->ic_bio.bi_opf |= REQ_PREFLUSH;
> >  
> > -	xlog_map_iclog_data(&iclog->ic_bio, iclog->ic_data, count);
> > +	xlog_map_iclog_data(iclog, count);
> >  	if (is_vmalloc_addr(iclog->ic_data))
> >  		flush_kernel_vmap_range(iclog->ic_data, count);
> >  
> > -- 
> > 2.21.1
> > 
>