[PATCH 1/3] xfs_repair: set NEEDSREPAIR the first time we write to a filesystem

Darrick J. Wong
2021-02-13T05:47:42Z

From: Darrick J. Wong <djwong@kernel.org>

Add a hook to the buffer cache so that xfs_repair can intercept the
first write to a V5 filesystem to set the NEEDSREPAIR flag. In the
event that xfs_repair dirties the filesystem and goes down, this ensures
that the sysadmin will have to re-start repair before mounting.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
---
include/xfs_mount.h | 4 ++
libxfs/rdwr.c | 4 ++
repair/xfs_repair.c | 95 +++++++++++++++++++++++++++++++++++++++++++++++++++
3 files changed, 103 insertions(+)

diff --git a/include/xfs_mount.h b/include/xfs_mount.h
index 75230ca5..f93a9f11 100644
--- a/include/xfs_mount.h
+++ b/include/xfs_mount.h
@@ -11,6 +11,8 @@ struct xfs_inode;
struct xfs_buftarg;
struct xfs_da_geometry;

+typedef void (*buf_writeback_fn)(struct xfs_buf *bp);
+
/*
* Define a user-level mount structure with all we need
* in order to make use of the numerous XFS_* macros.
@@ -95,6 +97,8 @@ typedef struct xfs_mount {
int qi_dqperchunk;
} *m_quotainfo;

+ buf_writeback_fn m_buf_writeback_fn;
+
/*
* xlog is defined in libxlog and thus is not intialized by libxfs. This
* allows an application to initialize and store a reference to the log
diff --git a/libxfs/rdwr.c b/libxfs/rdwr.c
index ac783ce3..ca272387 100644
--- a/libxfs/rdwr.c
+++ b/libxfs/rdwr.c
@@ -812,6 +812,10 @@ libxfs_bwrite(
return bp->b_error;
}

+ /* Trigger the writeback hook if there is one. */
+ if (bp->b_mount->m_buf_writeback_fn)
+ bp->b_mount->m_buf_writeback_fn(bp);
+
/*
* clear any pre-existing error status on the buffer. This can occur if
* the buffer is corrupt on disk and the repair process doesn't clear
diff --git a/repair/xfs_repair.c b/repair/xfs_repair.c
index 90d1a95a..12e319ae 100644
--- a/repair/xfs_repair.c
+++ b/repair/xfs_repair.c
@@ -720,6 +720,8 @@ clear_needsrepair(
struct xfs_buf *bp;
int error;

+ mp->m_buf_writeback_fn = NULL;
+
/*
* If we're going to clear NEEDSREPAIR, we need to make absolutely sure
* that everything is ok with the ondisk filesystem. Make sure any
@@ -751,6 +753,95 @@ clear_needsrepair(
libxfs_buf_relse(bp);
}

+static void
+update_sb_crc_only(
+ struct xfs_buf *bp)
+{
+ xfs_buf_update_cksum(bp, XFS_SB_CRC_OFF);
+}
+
+/* Forcibly write the primary superblock with the NEEDSREPAIR flag set. */
+static void
+force_needsrepair(
+ struct xfs_mount *mp)
+{
+ struct xfs_buf_ops fake_ops;
+ struct xfs_buf *bp;
+ int error;
+
+ if (!xfs_sb_version_hascrc(&mp->m_sb) ||
+ xfs_sb_version_needsrepair(&mp->m_sb))
+ return;
+
+ bp = libxfs_getsb(mp);
+ if (!bp || bp->b_error) {
+ do_log(
+ _("couldn't get superblock to set needsrepair, err=%d\n"),
+ bp ? bp->b_error : ENOMEM);
+ return;
+ } else {
+ /*
+ * It's possible that we need to set NEEDSREPAIR before we've
+ * had a chance to fix the summary counters in the primary sb.
+ * With the exception of those counters, phase 1 already
+ * ensured that the geometry makes sense.
+ *
+ * Bad summary counters in the primary super can cause the
+ * write verifier to fail, so substitute a dummy that only sets
+ * the CRC. In the event of a crash, NEEDSREPAIR will prevent
+ * the kernel from mounting our potentially damaged filesystem
+ * until repair is run again, so it's ok to bypass the usual
+ * verification in this one case.
+ */
+ fake_ops = xfs_sb_buf_ops; /* struct copy */
+ fake_ops.verify_write = update_sb_crc_only;
+
+ mp->m_sb.sb_features_incompat |=
+ XFS_SB_FEAT_INCOMPAT_NEEDSREPAIR;
+ libxfs_sb_to_disk(bp->b_addr, &mp->m_sb);
+
+ /* Force the primary super to disk immediately. */
+ bp->b_ops = &fake_ops;
+ error = -libxfs_bwrite(bp);
+ bp->b_ops = &xfs_sb_buf_ops;
+ if (error)
+ do_log(_("couldn't force needsrepair, err=%d\n"), error);
+ }
+ if (bp)
+ libxfs_buf_relse(bp);
+}
+
+/* Intercept the first write to the filesystem so we can set NEEDSREPAIR. */
+static void
+repair_capture_writeback(
+ struct xfs_buf *bp)
+{
+ struct xfs_mount *mp = bp->b_mount;
+ static pthread_mutex_t wb_mutex = PTHREAD_MUTEX_INITIALIZER;
+
+ /* Higher level code modifying a superblock must set NEEDSREPAIR. */
+ if (bp->b_ops == &xfs_sb_buf_ops || bp->b_bn == XFS_SB_DADDR)
+ return;
+
+ pthread_mutex_lock(&wb_mutex);
+
+ /*
+ * If someone else already dropped the hook, then needsrepair has
+ * already been set on the filesystem and we can unlock.
+ */
+ if (mp->m_buf_writeback_fn != repair_capture_writeback)
+ goto unlock;
+
+ /*
+ * If we get here, the buffer being written is not a superblock, and
+ * needsrepair needs to be set.
+ */
+ force_needsrepair(mp);
+ mp->m_buf_writeback_fn = NULL;
+unlock:
+ pthread_mutex_unlock(&wb_mutex);
+}
+
int
main(int argc, char **argv)
{
@@ -847,6 +938,10 @@ main(int argc, char **argv)
if (verbose > 2)
mp->m_flags |= LIBXFS_MOUNT_WANT_CORRUPTED;

+ /* Capture the first writeback so that we can set needsrepair. */
+ if (xfs_sb_version_hascrc(&mp->m_sb))
+ mp->m_buf_writeback_fn = repair_capture_writeback;
+
/*
* set XFS-independent status vars from the mount/sb structure
*/