There is a bug in the function nilfs_segctor_collect, which results in
active data being written to a segment, that is marked as clean. It is
possible, that this segment is selected for a later segment
construction, whereby the old data is overwritten.
The problem shows itself with the following kernel log message:
nilfs_sufile_do_cancel_free: segment 6533 must be clean
Usually a few hours later the file system gets corrupted:
NILFS: bad btree node (blocknr=8748107): level = 0, flags = 0x0,
nchildren = 0
NILFS error (device sdc1): nilfs_bmap_last_key: broken bmap
(inode number=114660)
The issue can be reproduced with a file system that is nearly full and
with the cleaner running, while some IO intensive task is running.
Although it is quite hard to reproduce.
This is what happens:
1. The cleaner starts the segment construction
2. nilfs_segctor_collect is called
3. sc_stage is on NILFS_ST_SUFILE and segments are freed
4. sc_stage is on NILFS_ST_DAT current segment is full
5. nilfs_segctor_extend_segments is called, which
allocates a new segment
6. The new segment is one of the segments freed in step 3
7. nilfs_sufile_cancel_freev is called and produces an error message
8. Loop around and the collection starts again
9. sc_stage is on NILFS_ST_SUFILE and segments are freed
including the newly allocated segment, which will contain active data
and can be allocated at a later time
10. A few hours later another segment construction allocates the segment
and causes file system corruption
This can be prevented by simply reordering the statements. If
nilfs_sufile_cancel_freev is called before nilfs_segctor_extend_segments
the freed segments are marked as dirty and cannot be allocated any more.
Signed-off-by: Andreas Rohner <andreas.rohner@xxxxxxx>
---
fs/nilfs2/segment.c | 10 ++++++----
1 file changed, 6 insertions(+), 4 deletions(-)
diff --git a/fs/nilfs2/segment.c b/fs/nilfs2/segment.c
index 9f6b486..a1a1916 100644
--- a/fs/nilfs2/segment.c
+++ b/fs/nilfs2/segment.c
@@ -1440,17 +1440,19 @@ static int nilfs_segctor_collect(struct nilfs_sc_info *sci,
nilfs_clear_logs(&sci->sc_segbufs);
- err = nilfs_segctor_extend_segments(sci, nilfs, nadd);
- if (unlikely(err))
- return err;
-
if (sci->sc_stage.flags & NILFS_CF_SUFREED) {
err = nilfs_sufile_cancel_freev(nilfs->ns_sufile,
sci->sc_freesegs,
sci->sc_nfreesegs,
NULL);
WARN_ON(err); /* do not happen */
+ sci->sc_stage.flags &= ~NILFS_CF_SUFREED;
}
+
+ err = nilfs_segctor_extend_segments(sci, nilfs, nadd);
+ if (unlikely(err))
+ return err;
+
nadd = min_t(int, nadd << 1, SC_MAX_SEGDELTA);
sci->sc_stage = prev_stage;
}
--
1.8.5.2
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