[PATCH 04/27] xfs: dispatch metadata scrub subcommands

Darrick J. Wong
2017-09-21T00:18:03Z

Create structures needed to hold scrubbing context and dispatch incoming
commands to the individual scrubbers.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
---
fs/xfs/scrub/scrub.c | 172 ++++++++++++++++++++++++++++++++++++++++++++++++++
fs/xfs/scrub/scrub.h | 19 ++++++
fs/xfs/scrub/trace.h | 43 +++++++++++++
3 files changed, 233 insertions(+), 1 deletion(-)

diff --git a/fs/xfs/scrub/scrub.c b/fs/xfs/scrub/scrub.c
index 5db2a6f..7cf518e 100644
--- a/fs/xfs/scrub/scrub.c
+++ b/fs/xfs/scrub/scrub.c
@@ -44,11 +44,181 @@
#include "scrub/scrub.h"
#include "scrub/trace.h"

+/*
+ * Online Scrub and Repair
+ *
+ * Traditionally, XFS (the kernel driver) did not know how to check or
+ * repair on-disk data structures. That task was left to the xfs_check
+ * and xfs_repair tools, both of which require taking the filesystem
+ * offline for a thorough but time consuming examination. Online
+ * scrub & repair, on the other hand, enables us to check the metadata
+ * for obvious errors while carefully stepping around the filesystem's
+ * ongoing operations, locking rules, etc.
+ *
+ * Given that most XFS metadata consist of records stored in a btree,
+ * most of the checking functions iterate the btree blocks themselves
+ * looking for irregularities. When a record block is encountered, each
+ * record can be checked for obviously bad values. Record values can
+ * also be cross-referenced against other btrees to look for potential
+ * misunderstandings between pieces of metadata.
+ *
+ * It is expected that the checkers responsible for per-AG metadata
+ * structures will lock the AG headers (AGI, AGF, AGFL), iterate the
+ * metadata structure, and perform any relevant cross-referencing before
+ * unlocking the AG and returning the results to userspace. These
+ * scrubbers must not keep an AG locked for too long to avoid tying up
+ * the block and inode allocators.
+ *
+ * Block maps and b-trees rooted in an inode present a special challenge
+ * because they can involve extents from any AG. The general scrubber
+ * structure of lock -> check -> xref -> unlock still holds, but AG
+ * locking order rules /must/ be obeyed to avoid deadlocks. The
+ * ordering rule, of course, is that we must lock in increasing AG
+ * order. Helper functions are provided to track which AG headers we've
+ * already locked. If we detect an imminent locking order violation, we
+ * can signal a potential deadlock, in which case the scrubber can jump
+ * out to the top level, lock all the AGs in order, and retry the scrub.
+ *
+ * For file data (directories, extended attributes, symlinks) scrub, we
+ * can simply lock the inode and walk the data. For btree data
+ * (directories and attributes) we follow the same btree-scrubbing
+ * strategy outlined previously to check the records.
+ *
+ * We use a bit of trickery with transactions to avoid buffer deadlocks
+ * if there is a cycle in the metadata. The basic problem is that
+ * travelling down a btree involves locking the current buffer at each
+ * tree level. If a pointer should somehow point back to a buffer that
+ * we've already examined, we will deadlock due to the second buffer
+ * locking attempt. Note however that grabbing a buffer in transaction
+ * context links the locked buffer to the transaction. If we try to
+ * re-grab the buffer in the context of the same transaction, we avoid
+ * the second lock attempt and continue. Between the verifier and the
+ * scrubber, something will notice that something is amiss and report
+ * the corruption. Therefore, each scrubber will allocate an empty
+ * transaction, attach buffers to it, and cancel the transaction at the
+ * end of the scrub run. Cancelling a non-dirty transaction simply
+ * unlocks the buffers.
+ *
+ * There are four pieces of data that scrub can communicate to
+ * userspace. The first is the error code (errno), which can be used to
+ * communicate operational errors in performing the scrub. There are
+ * also three flags that can be set in the scrub context. If the data
+ * structure itself is corrupt, the CORRUPT flag will be set. If
+ * the metadata is correct but otherwise suboptimal, the PREEN flag
+ * will be set.
+ */
+
+/* Scrub setup and teardown */
+
+/* Free all the resources and finish the transactions. */
+STATIC int
+xfs_scrub_teardown(
+ struct xfs_scrub_context *sc,
+ int error)
+{
+ if (sc->tp) {
+ xfs_trans_cancel(sc->tp);
+ sc->tp = NULL;
+ }
+ return error;
+}
+
+/* Scrubbing dispatch. */
+
+static const struct xfs_scrub_meta_ops meta_scrub_ops[] = {
+};
+
/* Dispatch metadata scrubbing. */
int
xfs_scrub_metadata(
struct xfs_inode *ip,
struct xfs_scrub_metadata *sm)
{
- return -EOPNOTSUPP;
+ struct xfs_scrub_context sc;
+ struct xfs_mount *mp = ip->i_mount;
+ const struct xfs_scrub_meta_ops *ops;
+ bool try_harder = false;
+ int error = 0;
+
+ trace_xfs_scrub_start(ip, sm, error);
+
+ /* Forbidden if we are shut down or mounted norecovery. */
+ error = -ESHUTDOWN;
+ if (XFS_FORCED_SHUTDOWN(mp))
+ goto out;
+ error = -ENOTRECOVERABLE;
+ if (mp->m_flags & XFS_MOUNT_NORECOVERY)
+ goto out;
+
+ /* Check our inputs. */
+ error = -EINVAL;
+ sm->sm_flags &= ~XFS_SCRUB_FLAGS_OUT;
+ if (sm->sm_flags & ~XFS_SCRUB_FLAGS_IN)
+ goto out;
+ if (memchr_inv(sm->sm_reserved, 0, sizeof(sm->sm_reserved)))
+ goto out;
+
+ /* Do we know about this type of metadata? */
+ error = -ENOENT;
+ if (sm->sm_type >= XFS_SCRUB_TYPE_NR)
+ goto out;
+ ops = &meta_scrub_ops[sm->sm_type];
+ if (ops->scrub == NULL)
+ goto out;
+
+ /* Does this fs even support this type of metadata? */
+ if (ops->has && !ops->has(&mp->m_sb))
+ goto out;
+
+ /* We don't know how to repair anything yet. */
+ error = -EOPNOTSUPP;
+ if (sm->sm_flags & XFS_SCRUB_IFLAG_REPAIR)
+ goto out;
+
+ /* This isn't a stable feature. Use with care. */
+ {
+ static bool warned;
+
+ if (!warned)
+ xfs_alert(mp,
+ "EXPERIMENTAL online scrub feature in use. Use at your own risk!");
+ warned = true;
+ }
+
+retry_op:
+ /* Set up for the operation. */
+ memset(&sc, 0, sizeof(sc));
+ sc.mp = ip->i_mount;
+ sc.sm = sm;
+ sc.ops = ops;
+ sc.try_harder = try_harder;
+ error = sc.ops->setup(&sc, ip);
+ if (error)
+ goto out_teardown;
+
+ /* Scrub for errors. */
+ error = sc.ops->scrub(&sc);
+ if (!try_harder && error == -EDEADLOCK) {
+ /*
+ * Scrubbers return -EDEADLOCK to mean 'try harder'.
+ * Tear down everything we hold, then set up again with
+ * preparation for worst-case scenarios.
+ */
+ error = xfs_scrub_teardown(&sc, 0);
+ if (error)
+ goto out;
+ try_harder = true;
+ goto retry_op;
+ } else if (error)
+ goto out_teardown;
+
+ if (sc.sm->sm_flags & (XFS_SCRUB_OFLAG_CORRUPT |
+ XFS_SCRUB_OFLAG_XCORRUPT))
+ xfs_alert_ratelimited(mp, "Corruption detected during scrub.");
+
+out_teardown:
+ error = xfs_scrub_teardown(&sc, error);
+out:
+ trace_xfs_scrub_done(ip, sm, error);
+ return error;
}
diff --git a/fs/xfs/scrub/scrub.h b/fs/xfs/scrub/scrub.h
index eb1cd9d..b271b2a 100644
--- a/fs/xfs/scrub/scrub.h
+++ b/fs/xfs/scrub/scrub.h
@@ -20,6 +20,25 @@
#ifndef __XFS_SCRUB_SCRUB_H__
#define __XFS_SCRUB_SCRUB_H__

+struct xfs_scrub_context;
+
+struct xfs_scrub_meta_ops {
+ int (*setup)(struct xfs_scrub_context *,
+ struct xfs_inode *);
+ int (*scrub)(struct xfs_scrub_context *);
+ bool (*has)(struct xfs_sb *);
+};
+
+struct xfs_scrub_context {
+ /* General scrub state. */
+ struct xfs_mount *mp;
+ struct xfs_scrub_metadata *sm;
+ const struct xfs_scrub_meta_ops *ops;
+ struct xfs_trans *tp;
+ struct xfs_inode *ip;
+ bool try_harder;
+};
+
/* Metadata scrubbers */

#endif /* __XFS_SCRUB_SCRUB_H__ */
diff --git a/fs/xfs/scrub/trace.h b/fs/xfs/scrub/trace.h
index a95a7c8..688517e 100644
--- a/fs/xfs/scrub/trace.h
+++ b/fs/xfs/scrub/trace.h
@@ -25,6 +25,49 @@

#include <linux/tracepoint.h>

+DECLARE_EVENT_CLASS(xfs_scrub_class,
+ TP_PROTO(struct xfs_inode *ip, struct xfs_scrub_metadata *sm,
+ int error),
+ TP_ARGS(ip, sm, error),
+ TP_STRUCT__entry(
+ __field(dev_t, dev)
+ __field(xfs_ino_t, ino)
+ __field(unsigned int, type)
+ __field(xfs_agnumber_t, agno)
+ __field(xfs_ino_t, inum)
+ __field(unsigned int, gen)
+ __field(unsigned int, flags)
+ __field(int, error)
+ ),
+ TP_fast_assign(
+ __entry->dev = ip->i_mount->m_super->s_dev;
+ __entry->ino = ip->i_ino;
+ __entry->type = sm->sm_type;
+ __entry->agno = sm->sm_agno;
+ __entry->inum = sm->sm_ino;
+ __entry->gen = sm->sm_gen;
+ __entry->flags = sm->sm_flags;
+ __entry->error = error;
+ ),
+ TP_printk("dev %d:%d ino %llu type %u agno %u inum %llu gen %u flags 0x%x error %d",
+ MAJOR(__entry->dev), MINOR(__entry->dev),
+ __entry->ino,
+ __entry->type,
+ __entry->agno,
+ __entry->inum,
+ __entry->gen,
+ __entry->flags,
+ __entry->error)
+)
+#define DEFINE_SCRUB_EVENT(name) \
+DEFINE_EVENT(xfs_scrub_class, name, \
+ TP_PROTO(struct xfs_inode *ip, struct xfs_scrub_metadata *sm, \
+ int error), \
+ TP_ARGS(ip, sm, error))
+
+DEFINE_SCRUB_EVENT(xfs_scrub_start);
+DEFINE_SCRUB_EVENT(xfs_scrub_done);
+
#endif /* _TRACE_XFS_SCRUB_TRACE_H */

#undef TRACE_INCLUDE_PATH