Re: [PATCH 03/14] xfs: repair the AGFL

[Brian Foster <bfoster@redhat.com>]

On Mon, Jul 30, 2018 at 10:22:16AM -0700, Darrick J. Wong wrote:
> On Mon, Jul 30, 2018 at 12:25:24PM -0400, Brian Foster wrote:
> > On Sun, Jul 29, 2018 at 10:48:08PM -0700, Darrick J. Wong wrote:
> > > From: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > Repair the AGFL from the rmap data.
> > > 
> > > Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > ---
> > 
> > FWIW, I tried tweaking a couple agfl values via xfs_db and xfs_scrub
> > seems to always dump a cross-referencing failed error and not want to
> > deal with it. Expected? Is there a good way to unit test some of this
> > stuff with simple/localized corruptions?
> 
> I usually pick one of the corruptions from xfs/355...
> 
> $ SCRATCH_XFS_LIST_FUZZ_VERBS=random \
> SCRATCH_XFS_LIST_METADATA_FIELDS=somefield \
> ./check xfs/355
> 

It looks like similar behavior if I do that, but tbh I'm not sure if I'm
using this correctly. E.g., if I do:

# SCRATCH_XFS_LIST_FUZZ_VERBS=random SCRATCH_XFS_LIST_METADATA_FIELDS=bno[0] ./check xfs/355
FSTYP         -- xfs (debug)
PLATFORM      -- Linux/x86_64 localhost 4.18.0-rc4+
MKFS_OPTIONS  -- -f -mrmapbt=1,reflink=1 /dev/mapper/test-scratch
MOUNT_OPTIONS -- -o context=system_u:object_r:root_t:s0 /dev/mapper/test-scratch /mnt/scratch

xfs/355 - output mismatch (see /root/xfstests-dev/results//xfs/355.out.bad)
    ...
    (Run 'diff -u tests/xfs/355.out /root/xfstests-dev/results//xfs/355.out.bad'  to see the entire diff)
Ran: xfs/355
Failures: xfs/355
Failed 1 of 1 tests
# diff -u tests/xfs/355.out /root/xfstests-dev/results//xfs/355.out.bad
--- tests/xfs/355.out   2018-07-25 07:47:23.739575416 -0400
+++ /root/xfstests-dev/results//xfs/355.out.bad 2018-07-31
10:55:18.466178944 -0400
@@ -1,6 +1,10 @@
 QA output created by 355
 Format and populate
 Fuzz AGFL
+online re-scrub (1) with bno[0] = random.
 Done fuzzing AGFL
 Fuzz AGFL flfirst
+offline re-scrub (1) with bno[14] = random.
+online re-scrub (1) with bno[14] = random.
+re-repair failed (1) with bno[14] = random.
 Done fuzzing AGFL flfirst

If I run xfs_scrub directly on the scratch mount after the test I get a
stream of inode cross-referencing errors and it doesn't seem to fix
anything up.

Brian

> > Otherwise this looks sane, a couple comments..
> > 
> > >  fs/xfs/scrub/agheader_repair.c |  276 ++++++++++++++++++++++++++++++++++++++++
> > >  fs/xfs/scrub/bitmap.c          |   92 +++++++++++++
> > >  fs/xfs/scrub/bitmap.h          |    4 +
> > >  fs/xfs/scrub/scrub.c           |    2 
> > >  4 files changed, 373 insertions(+), 1 deletion(-)
> > > 
> > > 
> > > diff --git a/fs/xfs/scrub/agheader_repair.c b/fs/xfs/scrub/agheader_repair.c
> > > index 4842fc598c9b..bfef066c87c3 100644
> > > --- a/fs/xfs/scrub/agheader_repair.c
> > > +++ b/fs/xfs/scrub/agheader_repair.c
> > > @@ -424,3 +424,279 @@ xrep_agf(
> > >  	memcpy(agf, &old_agf, sizeof(old_agf));
> > >  	return error;
> > >  }
> > > +
> > ...
> > > +/* Write out a totally new AGFL. */
> > > +STATIC void
> > > +xrep_agfl_init_header(
> > > +	struct xfs_scrub	*sc,
> > > +	struct xfs_buf		*agfl_bp,
> > > +	struct xfs_bitmap	*agfl_extents,
> > > +	xfs_agblock_t		flcount)
> > > +{
> > > +	struct xfs_mount	*mp = sc->mp;
> > > +	__be32			*agfl_bno;
> > > +	struct xfs_bitmap_range	*br;
> > > +	struct xfs_bitmap_range	*n;
> > > +	struct xfs_agfl		*agfl;
> > > +	xfs_agblock_t		agbno;
> > > +	unsigned int		fl_off;
> > > +
> > > +	ASSERT(flcount <= xfs_agfl_size(mp));
> > > +
> > > +	/* Start rewriting the header. */
> > > +	agfl = XFS_BUF_TO_AGFL(agfl_bp);
> > > +	memset(agfl, 0xFF, BBTOB(agfl_bp->b_length));
> > 
> > What's the purpose behind 0xFF? Related to NULLAGBLOCK/NULLCOMMITLSN..?
> 
> Yes, it prepopulates the AGFL bno[] array with NULLAGBLOCK, then writes
> in the header fields.
> 
> > > +	agfl->agfl_magicnum = cpu_to_be32(XFS_AGFL_MAGIC);
> > > +	agfl->agfl_seqno = cpu_to_be32(sc->sa.agno);
> > > +	uuid_copy(&agfl->agfl_uuid, &mp->m_sb.sb_meta_uuid);
> > > +
> > > +	/*
> > > +	 * Fill the AGFL with the remaining blocks.  If agfl_extents has more
> > > +	 * blocks than fit in the AGFL, they will be freed in a subsequent
> > > +	 * step.
> > > +	 */
> > > +	fl_off = 0;
> > > +	agfl_bno = XFS_BUF_TO_AGFL_BNO(mp, agfl_bp);
> > > +	for_each_xfs_bitmap_extent(br, n, agfl_extents) {
> > > +		agbno = XFS_FSB_TO_AGBNO(mp, br->start);
> > > +
> > > +		trace_xrep_agfl_insert(mp, sc->sa.agno, agbno, br->len);
> > > +
> > > +		while (br->len > 0 && fl_off < flcount) {
> > > +			agfl_bno[fl_off] = cpu_to_be32(agbno);
> > > +			fl_off++;
> > > +			agbno++;
> > 
> > 			/* bump br so we don't reap blocks we've used */
> > 
> > (i.e., took me a sec to realize why we bother with ->start)
> > 
> > > +			br->start++;
> > > +			br->len--;
> > > +		}
> > > +
> > > +		if (br->len)
> > > +			break;
> > > +		list_del(&br->list);
> > > +		kmem_free(br);
> > > +	}
> > > +
> > > +	/* Write new AGFL to disk. */
> > > +	xfs_trans_buf_set_type(sc->tp, agfl_bp, XFS_BLFT_AGFL_BUF);
> > > +	xfs_trans_log_buf(sc->tp, agfl_bp, 0, BBTOB(agfl_bp->b_length) - 1);
> > > +}
> > > +
> > ...
> > > diff --git a/fs/xfs/scrub/bitmap.c b/fs/xfs/scrub/bitmap.c
> > > index c770e2d0b6aa..fdadc9e1dc49 100644
> > > --- a/fs/xfs/scrub/bitmap.c
> > > +++ b/fs/xfs/scrub/bitmap.c
> > > @@ -9,6 +9,7 @@
> > >  #include "xfs_format.h"
> > >  #include "xfs_trans_resv.h"
> > >  #include "xfs_mount.h"
> > > +#include "xfs_btree.h"
> > >  #include "scrub/xfs_scrub.h"
> > >  #include "scrub/scrub.h"
> > >  #include "scrub/common.h"
> > > @@ -209,3 +210,94 @@ xfs_bitmap_disunion(
> > >  }
> > >  #undef LEFT_ALIGNED
> > >  #undef RIGHT_ALIGNED
> > > +
> > > +/*
> > > + * Record all btree blocks seen while iterating all records of a btree.
> > > + *
> > > + * We know that the btree query_all function starts at the left edge and walks
> > > + * towards the right edge of the tree.  Therefore, we know that we can walk up
> > > + * the btree cursor towards the root; if the pointer for a given level points
> > > + * to the first record/key in that block, we haven't seen this block before;
> > > + * and therefore we need to remember that we saw this block in the btree.
> > > + *
> > > + * So if our btree is:
> > > + *
> > > + *    4
> > > + *  / | \
> > > + * 1  2  3
> > > + *
> > > + * Pretend for this example that each leaf block has 100 btree records.  For
> > > + * the first btree record, we'll observe that bc_ptrs[0] == 1, so we record
> > > + * that we saw block 1.  Then we observe that bc_ptrs[1] == 1, so we record
> > > + * block 4.  The list is [1, 4].
> > > + *
> > > + * For the second btree record, we see that bc_ptrs[0] == 2, so we exit the
> > > + * loop.  The list remains [1, 4].
> > > + *
> > > + * For the 101st btree record, we've moved onto leaf block 2.  Now
> > > + * bc_ptrs[0] == 1 again, so we record that we saw block 2.  We see that
> > > + * bc_ptrs[1] == 2, so we exit the loop.  The list is now [1, 4, 2].
> > > + *
> > > + * For the 102nd record, bc_ptrs[0] == 2, so we continue.
> > > + *
> > > + * For the 201st record, we've moved on to leaf block 3.  bc_ptrs[0] == 1, so
> > > + * we add 3 to the list.  Now it is [1, 4, 2, 3].
> > > + *
> > > + * For the 300th record we just exit, with the list being [1, 4, 2, 3].
> > > + */
> > > +
> > > +/*
> > > + * Record all the buffers pointed to by the btree cursor.  Callers already
> > > + * engaged in a btree walk should call this function to capture the list of
> > > + * blocks going from the leaf towards the root.
> > > + */
> > > +int
> > > +xfs_bitmap_set_btcur_path(
> > > +	struct xfs_bitmap	*bitmap,
> > > +	struct xfs_btree_cur	*cur)
> > > +{
> > > +	struct xfs_buf		*bp;
> > > +	xfs_fsblock_t		fsb;
> > > +	int			i;
> > > +	int			error;
> > > +
> > > +	for (i = 0; i < cur->bc_nlevels && cur->bc_ptrs[i] == 1; i++) {
> > > +		xfs_btree_get_block(cur, i, &bp);
> > > +		if (!bp)
> > > +			continue;
> > > +		fsb = XFS_DADDR_TO_FSB(cur->bc_mp, bp->b_bn);
> > > +		error = xfs_bitmap_set(bitmap, fsb, 1);
> > 
> > Thanks for the comment. It helps explain the bc_ptrs == 1 check above,
> > but also highlights that xfs_bitmap_set() essentially allocates entries
> > for duplicate values if they exist. Is this handled by the broader
> > mechanism, for example, if the rmapbt was corrupted to have multiple
> > entries for a particular unused OWN_AG block? Or could we end up leaking
> > that corruption over to the agfl?
> 
> Right now we're totally dependent on the rmapbt being sane to rebuild
> the space metadata.
> 
> > I also wonder a bit about memory consumption on filesystems with large
> > metadata footprints. We essentially have to allocate one of these for
> > every allocation btree block before we can do the disunion and locate
> > the agfl-appropriate blocks. If we had a more lookup friendly structure,
> > perhaps this could be optimized by filtering out bnobt/cntbt blocks
> > during the associated btree walks..?
> > 
> > Have you thought about reusing something like the new in-core extent
> > tree mechanism as a pure in-memory extent store? It's certainly not
> > worth reworking something like that right now, but I wonder if we could
> > save memory via the denser format (and perhaps benefit from code
> > flexibility, reuse, etc.).
> 
> Yes, I was thinking about refactoring the iext btree into a more generic
> in-core index with 64-bit key so that I could adapt xfs_bitmap to use
> it.  In the longer term I would /also/ like to use xfs_bitmap to detect
> xfs_buf cache aliasing when multi-block buffers are in use, but that's
> further off. :)
> 
> As for the memory-intensive record lists in all the btree rebuilders, I
> have some ideas around that too -- either find a way to build an
> alternate btree and switch the roots over, or (once we gain the ability
> to mark an AG unavailable for new allocations) allocate an unlinked
> inode, store the records in the page cache pages for the file, and
> release it when we're done.
> 
> But, that can wait until I've gotten more of this merged, or get bored.
> :)
> 
> --D
> 
> > Brian
> > 
> > > +		if (error)
> > > +			return error;
> > > +	}
> > > +
> > > +	return 0;
> > > +}
> > > +
> > > +/* Collect a btree's block in the bitmap. */
> > > +STATIC int
> > > +xfs_bitmap_collect_btblock(
> > > +	struct xfs_btree_cur	*cur,
> > > +	int			level,
> > > +	void			*priv)
> > > +{
> > > +	struct xfs_bitmap	*bitmap = priv;
> > > +	struct xfs_buf		*bp;
> > > +	xfs_fsblock_t		fsbno;
> > > +
> > > +	xfs_btree_get_block(cur, level, &bp);
> > > +	if (!bp)
> > > +		return 0;
> > > +
> > > +	fsbno = XFS_DADDR_TO_FSB(cur->bc_mp, bp->b_bn);
> > > +	return xfs_bitmap_set(bitmap, fsbno, 1);
> > > +}
> > > +
> > > +/* Walk the btree and mark the bitmap wherever a btree block is found. */
> > > +int
> > > +xfs_bitmap_set_btblocks(
> > > +	struct xfs_bitmap	*bitmap,
> > > +	struct xfs_btree_cur	*cur)
> > > +{
> > > +	return xfs_btree_visit_blocks(cur, xfs_bitmap_collect_btblock, bitmap);
> > > +}
> > > diff --git a/fs/xfs/scrub/bitmap.h b/fs/xfs/scrub/bitmap.h
> > > index dad652ee9177..ae8ecbce6fa6 100644
> > > --- a/fs/xfs/scrub/bitmap.h
> > > +++ b/fs/xfs/scrub/bitmap.h
> > > @@ -28,5 +28,9 @@ void xfs_bitmap_destroy(struct xfs_bitmap *bitmap);
> > >  
> > >  int xfs_bitmap_set(struct xfs_bitmap *bitmap, uint64_t start, uint64_t len);
> > >  int xfs_bitmap_disunion(struct xfs_bitmap *bitmap, struct xfs_bitmap *sub);
> > > +int xfs_bitmap_set_btcur_path(struct xfs_bitmap *bitmap,
> > > +		struct xfs_btree_cur *cur);
> > > +int xfs_bitmap_set_btblocks(struct xfs_bitmap *bitmap,
> > > +		struct xfs_btree_cur *cur);
> > >  
> > >  #endif	/* __XFS_SCRUB_BITMAP_H__ */
> > > diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c
> > > index 1e8a17c8e2b9..2670f4cf62f4 100644
> > > --- a/fs/xfs/scrub/scrub.c
> > > +++ b/fs/xfs/scrub/scrub.c
> > > @@ -220,7 +220,7 @@ static const struct xchk_meta_ops meta_scrub_ops[] = {
> > >  		.type	= ST_PERAG,
> > >  		.setup	= xchk_setup_fs,
> > >  		.scrub	= xchk_agfl,
> > > -		.repair	= xrep_notsupported,
> > > +		.repair	= xrep_agfl,
> > >  	},
> > >  	[XFS_SCRUB_TYPE_AGI] = {	/* agi */
> > >  		.type	= ST_PERAG,
> > > 
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