Re: [PATCH 1/3] xfs_repair: set NEEDSREPAIR the first time we write to a filesystem
From: Brian Foster <hidden>
Date: 2021-02-16 11:57:27
On Fri, Feb 12, 2021 at 09:46:50PM -0800, Darrick J. Wong wrote:
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(+)
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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; +
Slight impedence mismatch in that we set the callback unconditionally (assuming crc=1) but we only get to this call if needsrepair is set.
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/* * 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);
This looks like it calls back into the writeback hook before it's been cleared. I'm guessing the xfs_sb_version_needsrepair() check above cuts off any recursion issues, but it might be cleaner to clear the callback pointer first.
+ 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);Doesn't appear we can get here with bp == NULL. Otherwise the rest looks reasonable to me. Brian
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+} + +/* 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 */