Re: [PATCH 0/9] xfs-5.0: inode scrubber fixes

[Chandan Rajendra <chandan@linux.ibm.com>]

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On Thursday, December 20, 2018 2:03:59 AM IST Darrick J. Wong wrote:
> On Wed, Dec 19, 2018 at 06:45:26PM +0530, Chandan Rajendra wrote:
> > On Wednesday, December 19, 2018 2:01:13 PM IST Chandan Rajendra wrote:
> > > On Thursday, November 29, 2018 4:56:58 AM IST Darrick J. Wong wrote:
> > > > Hi all,
> > > > 
> > > > Here are fixes for some problems with the inode btree scrub code, namely
> > > > that the existing code does not handle the case where a single inode
> > > > cluster is mapped by multiple inobt records.
> > > > 
> > > > Patch 1 teaches the inode record block counting code to handle the case
> > > > where there's more than one inobt record per inode cluster.  We do this
> > > > by counting inodes and converting to blocks only at the end.
> > > > 
> > > > Patch 2 corrects a condition where we needed to clamp the number of
> > > > inodes checked for a given inobt record to the inode chunk size.
> > > > 
> > > > Patches 3-4 move the inobt record alignment checks to a separate
> > > > function and enhance the function to check that when we have more than
> > > > one inobt record per cluster we actually check that *all* of the
> > > > necessary records are present and in the correct order.
> > > > 
> > > > Patches 5-7 reorganize the inobt free data checks to deal with the
> > > > "multiple inobt records per icluster" situation.  In restructuring the
> > > > code to do so, we also rename variables and functions to be less
> > > > confusing about what they're there for.  We also fix the 'is the inode
> > > > free?' check to calculate dinode buffer offsets correctly in the
> > > > "multiple inobt records per icluster" situation.
> > > > 
> > > > Patch 8 aborts the xattr scrub loop if there are pending fatal signals.
> > > > 
> > > > Patch 9 checks that for any directory or attr fork there are no extent
> > > > maps that stretch beyond what a xfs_dablk_t can map.
> > > > 
> > > > If you're going to start using this mess, you probably ought to just
> > > > pull from my git trees.  The kernel patches[1] should apply against
> > > > 4.20-rc4.
> > > > 
> > > > Comments and questions are, as always, welcome.
> > > 
> > > Hi Darrick,
> > > 
> > > I reviewed patches 1 through 7. The fixes look good.
> > > 
> > > I am not well versed with the XFS code that deals with xattrs &
> > > directories. Hence I could not review patches 8 and 9.
> > > 
> > > I did a simple scrub test on a 64k blocksized filesystem running a kernel
> > > having the following commit as the HEAD,
> > > 
> > > commit 6c4e1579b332e52566c11416e0dd0fa91a3b8f70 (HEAD -> djwong-devel, djwong-xfs-linux/djwong-devel)
> > > Author: Darrick J. Wong <darrick.wong@oracle.com>
> > > Date:   Thu Oct 18 17:35:49 2018 -0700
> > > 
> > >     xfs: repair quotas
> > >     
> > >     Fix anything that causes the quota verifiers to fail.
> > >     
> > >     Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > 
> > > Xfsprogs had the following as the topmost commit,
> > > 
> > > commit 633eec2a893c3be9796dad188144b00e084560ec (HEAD -> djwong-devel, djwong/djwong-devel)
> > > Author: Darrick J. Wong <darrick.wong@oracle.com>
> > > Date:   Tue Nov 13 17:38:31 2018 -0800
> > > 
> > >     xfs: repair extended attributes
> > >     
> > >     If the extended attributes look bad, try to sift through the rubble to
> > >     find whatever keys/values we can, zap the attr tree, and re-add the
> > >     values.
> > >     
> > >     Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
> > > 
> > > 
> > > The test filesystem had 2000 files with each being 64k in size.
> > > 
> > > root@ubuntu:~# xfs_scrub -d -n -v /mnt/
> > > EXPERIMENTAL xfs_scrub program in use! Use at your own risk!
> > > Phase 1: Find filesystem geometry.
> > > /mnt/: using 8 threads to scrub.
> > > Phase 2: Check internal metadata.
> > > Info: AG 1 superblock: Optimization is possible. (scrub.c line 269)
> > > Info: AG 3 superblock: Optimization is possible. (scrub.c line 269)
> > > Info: AG 2 superblock: Optimization is possible. (scrub.c line 269)
> > > Error: AG 0 free inode btree: Repairs are required. (scrub.c line 253)
> > > Phase 3: Scan all inodes.
> > > Phase 5: Check directory tree.
> > > Info: /mnt/: Filesystem has errors, skipping connectivity checks. (phase5.c line 295)
> > > Phase 7: Check summary counters.
> > > 163.9MiB data used;  1.9K inodes used.
> > > 152.7MiB data found; 1.9K inodes found.
> > > 1.9K inodes counted; 1.9K inodes checked.
> > > /mnt/: errors found: 1
> > > /mnt/: Re-run xfs_scrub without -n.
> > > 
> > > Looks like we have a bug when scrubbing the Free inode btree. I will work on
> > > figuring out the root cause and also plan to execute scrub tests shipped with
> > > xfstests.
> > > 
> > > 
> > 
> > We do have an unaligned finobt record,
> > 
> > xfs_scrub 27247 [004] 18014.774762: probe:xchk_iallocbt_rec_alignment: (c00000000075941c) ir_startino=176960 ig_cluster_align_inodes=128 imask_u32=127
> >         c00000000075941c xchk_iallocbt_rec_alignment+0x10c (/boot/vmlinux)
> >         c00000000075966c xchk_iallocbt_rec+0x14c (/boot/vmlinux)
> >                        0 [unknown] ([unknown])
> >         c000000000752968 xchk_btree+0x288 (/boot/vmlinux)
> >         c0000000007598c4 xchk_iallocbt+0x64 (/boot/vmlinux)
> >         c00000000075dc1c xfs_scrub_metadata+0x4ac (/boot/vmlinux)
> >         c0000000006e4b88 xfs_ioc_scrub_metadata+0x68 (/boot/vmlinux)
> >         c0000000006e7d5c xfs_file_ioctl+0xbbc (/boot/vmlinux)
> >         c000000000425e04 do_vfs_ioctl+0xd4 (/boot/vmlinux)
> >         c000000000426874 ksys_ioctl+0x64 (/boot/vmlinux)
> >         c000000000426928 __se_sys_ioctl+0x28 (/boot/vmlinux)
> >         c00000000000bae4 system_call+0x5c (/boot/vmlinux)
> >             7ffff77d7694 __GI___ioctl+0x114 (/lib/powerpc64le-linux-gnu/libc-2.27.so)
> >                10000e4e0 xfs_check_metadata+0x100 (/root/repos/xfsprogs-dev/scrub/xfs_scrub)
> >                10000e484 xfs_check_metadata+0xa4 (/root/repos/xfsprogs-dev/scrub/xfs_scrub)
> >                10000ec48 xfs_scrub_metadata+0xd8 (/root/repos/xfsprogs-dev/scrub/xfs_scrub)
> >                100008dac xfs_scan_ag_metadata+0x12c (/root/repos/xfsprogs-dev/scrub/xfs_scrub)
> >                1000198c8 workqueue_thread+0x108 (/root/repos/xfsprogs-dev/scrub/xfs_scrub)
> >             7ffff7f2885c start_thread+0x10c (/lib/powerpc64le-linux-gnu/libpthread-2.27.so)
> >             7ffff77e9028 __clone+0x98 (/lib/powerpc64le-linux-gnu/libc-2.27.so)
> > 
> > Maybe this is due to a bug in the finobt code. I will continue debugging and
> > report my findings.
> 
> Ok.  Feel free to send along a metadump if you have one.
> 


Indeed, XFS does not align finobt records according to inode cluster size.

More precisely, For big block filesystems, When freeing inodes (please refer
to xfs_difree_inobt()), XFS does not delete inobt records due to the following
code evaluating to false,

        if (!(mp->m_flags & XFS_MOUNT_IKEEP) &&
            rec.ir_free == XFS_INOBT_ALL_FREE &&
            mp->m_sb.sb_inopblock <= XFS_INODES_PER_CHUNK) {

However there is no such conditional check when deleting finobt records.
Hence I wrote the following patch,

---
 fs/xfs/libxfs/xfs_ialloc.c | 85 +++++++++++++++++++++++++++-----------
 fs/xfs/scrub/ialloc.c      |  2 +
 2 files changed, 64 insertions(+), 23 deletions(-)

diff --git a/fs/xfs/libxfs/xfs_ialloc.c b/fs/xfs/libxfs/xfs_ialloc.c
index f32be0c85f93..8d3edd758413 100644
--- a/fs/xfs/libxfs/xfs_ialloc.c
+++ b/fs/xfs/libxfs/xfs_ialloc.c
@@ -1399,14 +1399,19 @@ xfs_dialloc_ag_finobt_near(
 	struct xfs_btree_cur		*lcur = *ocur;	/* left search cursor */
 	struct xfs_btree_cur		*rcur;	/* right search cursor */
 	struct xfs_inobt_rec_incore	rrec;
+	xfs_agino_t			agino;
 	int				error;
 	int				i, j;
 
-	error = xfs_inobt_lookup(lcur, pagino, XFS_LOOKUP_LE, &i);
-	if (error)
-		return error;
+	agino = pagino;
+	while (1) {
+		error = xfs_inobt_lookup(lcur, agino, XFS_LOOKUP_LE, &i);
+		if (error)
+			return error;
+
+		if (i != 1)
+			break;
 
-	if (i == 1) {
 		error = xfs_inobt_get_rec(lcur, rec, &i);
 		if (error)
 			return error;
@@ -1417,23 +1422,39 @@ xfs_dialloc_ag_finobt_near(
 		 * only tracks chunks with at least one free inode, so record
 		 * existence is enough.
 		 */
-		if (pagino >= rec->ir_startino &&
-		    pagino < (rec->ir_startino + XFS_INODES_PER_CHUNK))
-			return 0;
+		if (rec->ir_freecount) {
+			if (pagino >= rec->ir_startino &&
+				pagino < (rec->ir_startino + XFS_INODES_PER_CHUNK))
+				return 0;
+			else
+				break;
+		}
+
+		agino = rec->ir_startino - 1;
 	}
 
 	error = xfs_btree_dup_cursor(lcur, &rcur);
 	if (error)
 		return error;
 
-	error = xfs_inobt_lookup(rcur, pagino, XFS_LOOKUP_GE, &j);
-	if (error)
-		goto error_rcur;
-	if (j == 1) {
+	agino = pagino;
+	while (1) {
+		error = xfs_inobt_lookup(rcur, agino, XFS_LOOKUP_GE, &j);
+		if (error)
+			goto error_rcur;
+
+		if (j != 1)
+			break;
+
 		error = xfs_inobt_get_rec(rcur, &rrec, &j);
 		if (error)
 			goto error_rcur;
 		XFS_WANT_CORRUPTED_GOTO(lcur->bc_mp, j == 1, error_rcur);
+
+		if (rrec.ir_freecount)
+			break;
+
+		agino = rrec.ir_startino + XFS_INODES_PER_CHUNK;
 	}
 
 	XFS_WANT_CORRUPTED_GOTO(lcur->bc_mp, i == 1 || j == 1, error_rcur);
@@ -1477,6 +1498,7 @@ xfs_dialloc_ag_finobt_newino(
 	struct xfs_btree_cur		*cur,
 	struct xfs_inobt_rec_incore	*rec)
 {
+	xfs_agino_t agino;
 	int error;
 	int i;
 
@@ -1490,22 +1512,32 @@ xfs_dialloc_ag_finobt_newino(
 			if (error)
 				return error;
 			XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
-			return 0;
+
+			if (rec->ir_freecount)
+				return 0;
 		}
 	}
 
 	/*
 	 * Find the first inode available in the AG.
 	 */
-	error = xfs_inobt_lookup(cur, 0, XFS_LOOKUP_GE, &i);
-	if (error)
-		return error;
-	XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
+	agino = 0;
+	while (1) {
+		error = xfs_inobt_lookup(cur, agino, XFS_LOOKUP_GE, &i);
+		if (error)
+			return error;
+		XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
 
-	error = xfs_inobt_get_rec(cur, rec, &i);
-	if (error)
-		return error;
-	XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
+		error = xfs_inobt_get_rec(cur, rec, &i);
+		if (error)
+			return error;
+		XFS_WANT_CORRUPTED_RETURN(cur->bc_mp, i == 1);
+
+		if (rec->ir_freecount)
+			break;
+
+		agino += XFS_INODES_PER_CHUNK;
+	}
 
 	return 0;
 }
@@ -1615,10 +1647,17 @@ xfs_dialloc_ag(
 	 */
 	rec.ir_free &= ~XFS_INOBT_MASK(offset);
 	rec.ir_freecount--;
-	if (rec.ir_freecount)
+	if (rec.ir_freecount) {
 		error = xfs_inobt_update(cur, &rec);
-	else
-		error = xfs_btree_delete(cur, &i);
+	} else {
+		if (!(mp->m_flags & XFS_MOUNT_IKEEP) &&
+			/* TODO: Add a condition to check hole mask */
+			mp->m_sb.sb_inopblock <= XFS_INODES_PER_CHUNK)
+			error = xfs_btree_delete(cur, &i);
+		else
+			error = xfs_inobt_update(cur, &rec);
+	}
+
 	if (error)
 		goto error_cur;
 
diff --git a/fs/xfs/scrub/ialloc.c b/fs/xfs/scrub/ialloc.c
index 9269f5158cdc..838161f25db4 100644
--- a/fs/xfs/scrub/ialloc.c
+++ b/fs/xfs/scrub/ialloc.c
@@ -79,9 +79,11 @@ xchk_iallocbt_chunk_xref_other(
 	error = xfs_ialloc_has_inode_record(*pcur, agino, agino, &has_irec);
 	if (!xchk_should_check_xref(sc, &error, pcur))
 		return;
+#if 0
 	if (((irec->ir_freecount > 0 && !has_irec) ||
 	     (irec->ir_freecount == 0 && has_irec)))
 		xchk_btree_xref_set_corrupt(sc, *pcur, 0);
+#endif
 }
 
 /* Cross-reference with the other btrees. */
-- 

The "cross reference" check had to be disabled since the above patch now
causes finobt entries with freecount value set to be 0 in big block
filesystem instances.

The following trivial tests have been executed on a kernel compiled with the
above patch,

1. For both 4k and 64k block sized filesystems,
   1. Create 2000 files and execute xfs_scrub.
2. Repeat step 1 with sparse inode feature disabled.
3. Build linux kernel on the test filesystem.

I am planning to test it more thoroughly after I get review comments for the
code changes provided above.

I have attached xz compressed image of xfs_metadump output of the test
filesystem along with this mail.

PS: Apologies for the delayed response. It took me some time to understand the
relevant code and write the patch provided above.

-- 
chandan

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